National Academies Press: OpenBook

Highway and Street Design Vehicles: An Update (2023)

Chapter: Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles

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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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Suggested Citation:"Chapter 5 - Updated Dimensions and Recommended Additions to the Green Book Design Vehicles." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
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36 This chapter presents the current AASHTO design vehicles for each vehicle type and class, summarizes available data about the current vehicle fleet, recommends updates to the dimen- sions of the Green Book design vehicles for consideration by AASHTO, and recommends one addition to the set of Green Book design vehicles for consideration by AASHTO. 5.1 Overview of Design Vehicles Each design vehicle presented in the Green Book is intended to represent, for geometric design purposes, an entire class of vehicles in the vehicle fleet. The design vehicle is not necessarily the largest in its class but is typically one of the larger vehicles in the class. Each design vehicle is intended to represent a vehicle that is sufficiently common in the traffic stream that it can serve as a basis for designing facilities to accommodate that vehicle class on roadways. Use of such a design vehicle should result in larger vehicles in that vehicle class being likely to traverse the roadway only occasionally. Where a full quantitative distribution of key vehicle dimensions is available, it is reasonable for a design vehicle to fall within the 90th to 95th percentile in size for vehicles of the class that the design vehicle represents. Thus, design vehicles are by their nature a conservative choice, since they represent a substantial majority of a given vehicle class. Design vehicles should not be too conservative (i.e., larger than any vehicle in the class). The dimensions of design vehicles currently recommended in the Green Book are presented in Table 1 and are illustrated in figures presented in this chapter (AASHTO 2018). The terminology used in design vehicle dimensions has been defined in Figures 3 through 9 and in the discussion in Section 2.2. This chapter presents what is currently known about each of the vehicle classes that the design vehicles represent. This chapter also recommends appropriate updates to the dimensions of the design vehicles to better match the current vehicle fleet. The turning perfor- mance of the updated design vehicles is presented in Chapter 6. The application of the design vehicles in geometric design is addressed in Chapter 7. Each vehicle class includes vehicles with a broad range of sizes. Thus, no design vehicle can be equivalent in size and turning performance to all vehicles in its class. Rather, because a design vehicle represents a larger vehicle within its class, a designer can presume that if a specific facility is designed to accommodate a given design vehicle, then the vast majority of vehicles within that class (and virtually all vehicles in smaller vehicle classes) will be able to use that facility in the manner intended by the designer (see further discussion in Chapter 7). 5.2 Passenger Vehicles The current Green Book includes one passenger car design vehicle, shown in Figure 15. The design vehicle is shown in the figure as a four-door sedan, but it is intended to represent, for C H A P T E R 5 Updated Dimensions and Recommended Additions to the Green Book Design Vehicles

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 37 design purposes, all private passenger vehicles, including two-door sedans, two-door coupes, four- door sedans, station wagons, minivans and vans, sport utility vehicles (SUVs), and pickup trucks. Some of the vans and pickup trucks are designed to transport cargo but are classified here as pas- senger vehicles because many people use them for personal transportation. Some van models with nearly identical exterior dimensions are sold in both cargo- and passenger-transportation versions. The Green Book uses an overall width of 7.0 ft and a track width of 6.0 ft for the P design vehicle. Table 1 indicates that the P design vehicle has an overall height of 4.3 ft. The research has considered whether the current dimensions of the P design vehicle shown in Table 1 and Figure 15 are appropriate to represent current passenger vehicles in road design. As noted in Chapter 4, a data set has been compiled with dimensions of all 2019 model passenger vehicles being manufactured and/or sold in the United States. This data set includes dimensions for 205 combinations of vehicle make and model. All the passenger vehicles con- sidered have a maximum GVW less than or equal to 10,000 lb, since vehicles with GVW greater than 10,000 lb are considered to be heavy trucks or other commercial vehicles. Only vans that transport eight passengers or less were included. Table 18 summarizes the data obtained on the distribution of overall vehicle lengths for 2019 model passenger vehicles. The table includes dimensions for passenger vehicles as a whole and for specific types of passenger vehicles, including minivans and vans; pickup trucks; auto- mobiles (sedans, coupes, convertibles, station wagons); sports cars; and SUVs. The table is based on data for specific 2019 models and does not reflect which models had the greatest or least sales or are driven the most or least vehicle miles. The table shows that 2019 passenger vehicle models range in overall length from 11.93 ft to 20.88 ft. The 90th percentile passenger vehicle model is 18.49 ft in overall length, while the 95th percentile passenger vehicle model is 19.31 ft in overall length. In comparison, the P design vehicle has an overall length of 19 ft, which falls between the 90th and 95th percentile of the 2019 passenger vehicle models manufactured and/or sold in the United States. The table shows that all 2019 automobiles (sedans, coupes, convertibles, station wagons), sports cars, and SUVs are less than 19 ft in length. Only vans and pickup trucks have overall lengths that exceed 19 ft. A total of 16 out of the total of 205 passenger vehicle models for the model year 2019 have overall lengths that exceed 19 ft. Table 18 shows that only 7.6% of passenger vehicles exceed 19 ft in length, but 23% of vans and 81% of pickup trucks exceed 19 ft in length. Table 19 shows the dimensions for these 16 passenger vehicle models, including 3 vans and 13 pickup truck models. The three van models that exceed 19 ft in overall length are all configured for cargo transportation with three doors and two passenger seats, one for a driver and one for a front-seat passenger. The pickup trucks are models that may be used for cargo transportation but are often used for personal transportation. Source: AASHTO 2018. Figure 15. Dimensions of current passenger car (P) design vehicle.

Passenger car type Number of models Vehicle length (ft) for specific passenger vehicle models Percent of passenger vehicle models for specific vehicle length ranges (ft) Minimum Mean 90th percentile 95th percentile Maximum ≤ 17 > 17 to 18 > 18 to 19 > 19 All types combined 205 11.93 15.94 18.49 19.31 20.88 83.4 5.4 3.4 7.6 Automobilesa 99 11.93 15.36 16.55 16.82 17.40 97.0 3.0 0.0 0.0 Minivans/vans 13 14.52 17.34 19.67 20.88 20.88 61.5 0.0 15.4 23.1 Pickup trucks 16 17.44 19.17 20.21 20.83 20.83 0.0 18.8 0.0 81.2 Sports cars 12 12.84 14.46 15.43 15.69 15.69 100.0 0.0 0.0 0.0 SUVs 65 13.44 16.03 17.50 18.49 18.70 84.6 7.7 7.7 0.0 a Sedans, coupes, convertibles, and station wagons. SUV = Sport utility vehicle. Vehicle length represents the length of the vehicle body (not including appurtenances such as bicycle racks or trailer hitches). Table 18. Summary of overall vehicle lengths for all 2019 passenger vehicle models.

Vehicle make Vehicle model Vehicle type Number of Vehicle dimensions (ft) Turning circle (ft)Doors Passengers Overalllength Wheelbase Width Height Ground clearance Ram Promaster Extended Van 3 2 20.88 13.25 6.89 8.42 0.58 46.8 Ford Super DutyF-250 Pickup truck 4 5 20.83 13.33 6.67 6.53 0.68 54.7 Ford F-150Supercrew Pickup truck 4 5 20.31 13.07 6.66 6.43 0.78 51.1 Chevrolet Silverado 2500 HD Pickup truck 4 5 19.96 12.81 6.71 6.52 0.81 51.5 GMC Sierra 2500 HD Pickup truck 4 5 19.86 12.81 6.71 6.52 0.81 51.5 Ram Promaster Van 3 2 19.67 11.33 6.73 8.28 0.58 40.7 Ford Transit Van 148 Van 3 2 19.63 12.30 6.78 8.39 — 47.8 Ford F-150Supercab Pickup truck 4 5 19.33 12.08 6.66 6.43 0.78 47.1 Ram 1500 Pickup truck 4 6 19.33 11.71 6.84 6.47 0.73 46.2 Chevrolet Silverado 1500 Pickup truck 4 6 19.31 12.29 6.77 6.29 0.68 46.9 GMC Sierra 1500 Pickup truck 4 5 19.31 12.28 6.77 6.29 0.68 46.3 GMC Sierra 1500 Limited Pickup truck 4 6 19.31 11.96 6.67 6.16 0.66 46.4 Chevrolet Silverado 1500 LD Pickup truck 4 6 19.17 11.96 6.67 6.16 0.74 46.9 Ram 1500 Classic Pickup truck 4 6 19.08 11.67 6.62 6.41 0.72 45.1 Toyota Tundra Pickup truck 4 5 19.08 12.14 6.66 6.35 0.88 44.0 Toyota Tundra 2WD Pickup truck 4 5 19.08 12.14 6.66 6.32 0.88 44.0 Table 19. Summary of dimensions for all 2019 passenger vehicles that exceed 19 ft in overall length.

40 Highway and Street Design Vehicles: An Update The P design vehicle has a wheelbase of 11 ft. Table 20 shows that only 8% of passenger vehicles have wheelbases that exceed 11 ft in length. All automobiles (sedans, coupes, convertibles, station wagons), sports cars, and SUVs have wheelbases less than 11 ft in length. The vans and pickup trucks with wheelbases that exceed 11 ft are essentially the same vehicles shown in Table 19. The P design vehicle has an overall width of 7 ft. Table 21 shows that every 2019 model passenger vehicle, including vans and pickup trucks, has an overall width of less than 7 ft. This might imply that a design vehicle with a width of less than 7 ft could be used. However, the Green Book consistently rounds maximum vehicle widths up to the next even 0.5 ft, so a P design vehicle with a 7-ft length is appropriate. The overall height of the P design vehicle is 4.3 ft. Table 22 shows that the minimum height of a 2019 model passenger vehicle is 4.22 ft. Automobiles (sedans, coupes, convertibles, station wagons) have heights up to 5.75 ft, while SUVs and pickup trucks have maximum heights of 6.43 ft and 6.53 ft, respectively. Some vans have overall heights of up to 8.42 ft. Tables 18 through 22, and subsequent tables like them based on manufacturers’ data, give equal weight to each vehicle make and model, regardless of the number of vehicles sold or the miles driven for that particular make and model. Data on sales by vehicle make and model are proprietary and cannot be readily obtained. Data on the number of miles driven per year for specific vehicle makes and models are also unavailable. The data presented show that automobiles and larger passenger vehicles, particularly pickup trucks, are distinctly different in size. Automobiles are generally smaller than the current P design vehicle and pickup trucks are often larger than the current P design vehicle. Given that auto- mobiles now constitute only about one-half of registered vehicles and pickup trucks constitute over 40% of passenger vehicles (see Table 17), a design vehicle for a passenger vehicle larger than an automobile appears to be needed. On the other hand, there may be situations where the design for an automobile is appropriate, but the design vehicle representing an automobile should be appropriate in size for the automobile fleet currently on the road. Therefore, it is recommended that the current P design vehicle be replaced with two updated design vehicles: a smaller design vehicle representing an automobile (which will continue to be designated as the P design vehicle) and a larger design vehicle representing a pickup truck (to be designated as the PU design vehicle). The updated P design vehicle is recommended to be 16.8 ft in total length, with a wheelbase of 9.8 ft, a front overhang of 3.0 ft, and a rear overhang of 4.0 ft. This is just below the 95th per- centile for current automobile lengths. The typical height for an automobile of this size is 5.5 ft. The current design vehicle width of 7.0 ft is recommended for retention. The recommended dimensions for the updated P design vehicle are presented in Figure 16. The new PU design vehicle is recommended to be 20.3 ft in total length, with a wheelbase of 13.0 ft, a front overhang of 3.2 ft, and a rear overhang of 4.1 ft. This is between the 90th and 95th percentiles for current pickup truck lengths. The typical height for a pickup truck of this size is 6.5 ft. A design vehicle width of 7.0 ft is recommended for use. The recommended dimen- sions for the new PU design vehicle are presented in Figure 17. 5.3 Single-Unit Trucks The Green Book includes two design vehicles representing single-unit trucks, also known as straight trucks: • SU-30—Single-Unit Truck (two-axle) (see Figure 18) • SU-40—Single-Unit Truck (three-axle) (see Figure 19) Each of these design vehicles is discussed below.

Passenger vehicle type Number of models Wheelbase (ft) for specific passenger vehicle models Percent of passenger vehicle models for specific wheelbase ranges (ft) Minimum Mean 90th percentile 95th percentile Maximum ≤ 10 > 10 to 11 > 11 to 12 > 12 All types combined 205 7.58 9.49 10.83 12.08 13.33 79.0 13.2 2.6 5.4 Automobilesa 99 7.83 9.13 9.81 10.02 10.53 93.9 6.1 0.0 0.0 Minivans/vans 13 8.73 10.55 12.30 13.25 13.25 30.8 46.1 9.7 15.4 Pickup trucks 16 10.20 11.91 12.81 13.33 13.33 0.0 18.8 25.0 56.2 Sports cars 12 7.58 8.36 8.96 9.18 9.18 100.0 0.0 0.0 0.0 SUVs 65 8.27 9.44 10.21 10.83 10.97 81.5 18.5 0.0 0.0 a Sedans, coupes, convertibles, and station wagons. SUV = Sport utility vehicle. Table 20. Summary of wheelbases for all 2019 passenger vehicle models. Passenger vehicle type Number of models Vehicle width (ft) for specific passenger vehicle models Percent of passenger vehicle models for specific width ranges (ft) Minimum Mean 90th percentile 95th percentile Maximum ≤ 5.5 > 5.5 to 6 > 6 to 6.5 > 6.5 All types combined 201 5.23 6.21 6.67 6.71 6.97 0.5 22.4 53.2 33.9 Automobilesa 98 5.23 6.03 6.27 6.35 6.69 1.0 35.7 61.3 2.0 Minivans/vans 11 5.68 6.54 6.78 6.89 6.89 0.0 9.1 9.1 81.8 Pickup trucks 16 6.19 6.65 6.77 6.84 6.84 0.0 0.0 6.3 93.7 Sports cars 11 5.69 6.12 6.38 6.45 6.45 0.0 27.3 72.7 0.0 SUVs 65 5.65 6.34 6.71 6.71 6.97 0.0 9.2 57.0 33.8 a Sedans, coupes, convertibles, and station wagons. SUV = Sport utility vehicle. Vehicle width represents the width of the vehicle body (not including appurtenances such as mirrors). Table 21. Summary of overall vehicle widths for all 2019 passenger vehicle models. Passenger vehicle type Number of models Vehicle height (ft) for specific passenger vehicle models Percent of passenger vehicle models for specific vehicle height ranges (ft) Minimum Mean 90th percentile 95th percentile Maximum ≤ 5 > 5 to 6 > 6 to 6.5 > 6.5 All types combined 204 3.88 5.31 6.29 6.43 8.42 48.5 32.9 14.7 3.9 Automobilesa 99 4.22 4.81 5.26 5.51 5.75 83.4 16.6 0.0 0.0 Minivans/vans 13 5.66 6.86 8.40 8.42 8.42 0.0 30.8 30.7 38.5 Pickup trucks 16 5.89 6.32 6.52 6.53 6.53 0.0 12.5 68.7 18.8 Sports cars 12 3.88 4.26 4.56 4.63 4.63 100.0 0.0 0.0 0.0 SUVs 64 4.61 5.70 6.20 6.37 6.43 4.7 71.9 23.4 0.0 a Sedans, coupes, convertibles, and station wagons. SUV = Sport utility vehicle. Vehicle height represents the height of the vehicle body (not including appurtenances such as roof racks). Table 22. Summary of overall vehicle heights for all 2019 passenger vehicle models.

42 Highway and Street Design Vehicles: An Update Figure 16. Dimensions of updated passenger car (P) design vehicle. Figure 17. Dimensions of new pickup truck (PU) design vehicle. Source: AASHTO 2018. Figure 18. Dimensions of two-axle single-unit truck design vehicle (SU-30).

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 43 5.3.1 Two-Axle Single-Unit Truck The dimensions of the two-axle single-unit truck (SU-30) design vehicle are illustrated in Figure 18. The two axles on this design vehicle consist of a single steering axle at the front of the vehicle and a single rear axle. This design vehicle has an overall length of 30 ft and a wheelbase of 20 ft. The width of the design vehicle is 8 ft. The track width of the SU-30 design vehicle is not explicitly stated in the Green Book but appears to be the same as the overall vehicle width. The overall vehicle height is 11 ft to 13.5 ft. The design vehicle drawing in Figure 18 shows the cargo area as an enclosed van, but this vehicle merely represents, for geometric design purposes, the many types of cargo areas found on single-unit trucks. 5.3.2 Three-Axle Single-Unit Truck The dimensions of the three-axle single-unit truck (SU-40) design vehicle are illustrated in Figure 19. The three axles on the vehicle consist of a single steering axle at the front of the vehicle and tandem rear axles. This design vehicle has an overall length of 39.5 ft and a wheelbase of 25 ft. The width of the design vehicle is 8 ft. The track width of the SU-40 design vehicle is not explicitly stated in the Green Book but appears to be the same as the overall vehicle width. The overall vehicle height is 11 ft to 13.5 ft. The design vehicle drawing in Figure 19 shows the cargo area as an enclosed van, but this vehicle merely represents, for geometric design purposes, the many types of cargo areas found on single-unit trucks. A three-axle single-unit truck would typically be used by a truck operator to carry cargo with greater density than a two-axle single- unit truck. Under the normal federal weight limits that apply on interstate highways, a two-axle single-unit truck can carry 36,000 lb (vehicle plus cargo weight), while a three-axle single-unit truck with an appropriately distributed load can carry 52,000 lb. 5.3.3 Size Limits for Single-Unit Trucks There are no size limits for single-unit trucks established at the federal level. Twenty-four states and the District of Columbia have a maximum limit of 40 ft for the overall length of a single-unit truck, approximately equivalent to the length of the SU-40 design vehicle. The remaining states have length limits larger than 40 ft, ranging from 42 ft to 60 ft. The most common of these larger length limits is 45 ft, which is applicable in 19 states. Source: AASHTO 2018. Figure 19. Dimensions of three-axle single-unit truck design vehicle (SU-40).

44 Highway and Street Design Vehicles: An Update 5.3.4 Single-Unit Trucks Currently Manufactured or Sold in the United States Most single-unit trucks sold in the United States have a specific wheelbase stated in the manufac- turers’ literature. However, a few single-unit truck models can be custom ordered with a wheel- base within a broad range. Table 23 summarizes selected dimensions for single-unit trucks currently being manufactured or sold in the United States. These data were assembled from manufacturers’ data for trucks sold in the United States. Table 23 shows the distribution of wheelbases for single-unit truck models for which the wheelbase has a fixed length (i.e., single-unit trucks that cannot be ordered with a range of wheelbases). The table shows that the wheelbases vary from 9.08 ft to 26.00 ft, with a 90th percentile value of 20.90 ft and a 95th percentile value of 22.08 ft. Only 17 models of single-unit trucks are sold with variable wheelbases that can be custom ordered, as compared to 914 single-unit truck models with fixed wheelbases. The wheelbases of these custom-ordered single-unit trucks may range from 11.5 ft to 37.33 ft. While these custom- ordered wheelbases can be up to 11.33 ft longer than the single-unit truck models with fixed wheel- bases shown in Table 23, it appears unlikely that these 17 particular models (less than 2% of the single-unit truck models on the market) with wheelbases longer than those of the SU-40 design vehicle constitute a substantial portion of the vehicle fleet. Trucks with these longer wheelbases are likely intended for use in the states that permit such long wheelbases for single-unit trucks. Table 23 shows that there are a few single-unit trucks with four or five axles on the market, but most single-unit trucks have two or three axles, which correspond to the SU-30 and SU-40 design vehicles. Based on the data presented in Table 23, it appears that both a two- and a three-axle single-unit truck should be retained in the Green Book as design vehicles. The two-axle single-unit trucks in today’s market appear to be longer than the current SU-30 design vehicle. Table 23 shows that the 95th percentile length for a two-axle single-unit truck is approximately 22 ft. However, Table 23 includes only single-unit truck models with a fixed-length wheelbase. Since other truck models are sold with longer custom-ordered wheelbases, the wheelbase for the two-axle single- unit truck was set at 23 ft (i.e., 3 ft longer than the current SU-30 wheelbase of 20 ft). Thus, it is recommended that the SU-30 design vehicle be replaced with a design vehicle that is 3 ft longer (to be designated as the SU-33 design vehicle). The dimensions of the recommended SU-33 design vehicle are presented in Figure 20. As in the case of two-axle single-unit trucks, some models of three-axle single-unit trucks can be custom ordered with longer wheelbases. Therefore, there does not appear to be any reason to change the dimensions of the current SU-40 design vehicle, which should remain as shown in Figure 19. The height and width of both SU design vehicles remain unchanged. Number of axles Number of models Wheelbase (ft) for single-unit truck models for which the wheelbase does not vary Minimum Mean 90thpercentile 95th percentile Maximum All types combined 914 9.08 15.89 20.90 22.08 26.00 Two axles 787 9.08 15.74 20.67 21.92 24.69 Three axles 85 12.50 16.48 20.78 21.33 22.83 Four axles 41 12.50 17.60 22.08 22.83 26.00 Five axles 1 14.25 14.25 14.25 14.25 14.25 Table 23. Wheelbase dimensions for single-unit truck models for which the wheelbase has a fixed length.

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 45 Figure 20. Recommended dimensions for updated two-axle single-unit truck design vehicle (SU-33). 5.4 Tractors for Use in Combination Trucks Combination trucks, including single-, double-, and triple-trailer trucks (discussed in Sec- tions 5.5, 5.6, and 5.7, respectively), consist of one to three trailers pulled by a special-purpose power unit known as a tractor. A tractor typically consists of a cab in which the driver is seated, an engine that provides the power to propel the vehicle (typically located in front of the cab), and a frame extending behind the cab on which the hitch to connect a trailer is mounted. Some tractors include a sleeping area behind the cab where a driver can take required off-duty rest breaks. A tractor with no trailer(s) attached is a single-unit truck, and many of the single-unit trucks shown in manufacturers’ literature can also be configured as tractors. Before the passage of the 1982 STAA, many states imposed overall length limits on combi- nation trucks. This created an economic incentive for truck operators to use tractors as short as practical, such as cab-over-engine designs, so that the cargo-carrying (CC) area could be as long as practical. The 1982 STAA prohibited states from establishing overall truck length limits for tractor-trailer combination trucks and replaced them with limits on the maximum lengths of trailers. This removed the incentive toward shorter tractors and allowed truck operators to use a tractor of any length in a tractor-trailer combination truck. Therefore, cab-over-engine tractors are no longer common as they once were. Truck operators likely continue to use shorter cab-behind-engine tractors for short trips, such as within city operations, and for lighter loads, while longer tractors are typically used for over-the-road operations and heavier loads. Figure 21 shows the dimensions of tractors used in the current Green Book design vehicles: • The WB-40 intermediate semitrailer truck discussed in Section 5.5 uses the smaller two-axle conventional tractor shown in Figure 21B. • The WB-62 and WB-67 interstate semitrailers discussed in Section 5.5 use the conventional long-haul tractor shown in Figure 21B. • The WB-67D and WB-100T double- and triple-trailer trucks discussed in Sections 5.6 and 5.7 use the cab-over-engine tractor shown in Figure 21C. • The WB-92D Rocky Mountain double-trailer truck discussed in Section 5.6 uses the con- ventional tractor shown in Figure 21D. • The WB-109D turnpike double-trailer truck discussed in Section 5.6 uses the cab-over-engine tractor shown in Figure 21D. Unlike passenger cars, manufacturers’ data for tractors are not very informative for the current research because many tractor models can be custom ordered from the manufacturer with a

46 Highway and Street Design Vehicles: An Update Source: AASHTO 2018. Figure 21. Dimensions of typical tractors for combination trucks.

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 47 range of wheelbases to fit the truck operator’s needs and the regulatory environment in which the truck will be used. For example, one particular tractor model can be ordered with wheel- bases up to 40.5 ft. However, tractors with wheelbases as long as 40.5 ft are rarely seen on the road and would likely be purchased only for special applications. Because of the substantial variation in the dimensions of custom-ordered tractors, the dimen- sions of tractors for combination trucks could not be compiled from manufacturers’ litera- ture. Therefore, results from the field studies described in Section 4.3 were used to estimate the dimensions of tractors used with specific combination truck types. Tractors for five-axle single- and double-trailer trucks should represent large, but not necessarily the largest, tractors observed in the field data. By contrast, a city or short-haul tractor should represent a small, but not necessarily the smallest, four-axle tractor observed in the field data. This investigation found the following: • Long-haul tractors have increased in length such that a tractor wheelbase of 21.0 ft, rather than 19.5 ft, is now appropriate; this 21.0-ft wheelbase falls between the 90th percentile wheelbase of 20.8 ft and the 95th percentile wheelbase of 21.5 ft for tractors for five-axle single-tractor trucks with van trailers. • City or short-haul tractors have increased only slightly in length such that a tractor wheelbase of 12.9 ft, rather than 12.5 ft, is now appropriate; the 12.9-ft wheelbase for the city or short- haul tractor represents both the 10th percentile and 15th percentile of observed wheelbases for tractors of four-axle single-trailer trucks with van trailers. • Cab-over-engine tractors are no longer in common use for double- and triple-trailer trucks. The typical tractor for a double- or triple-trailer combination truck with 28.5-ft trailers is a short cab-behind-engine tractor with a 15.0-ft tractor wheelbase, in contrast to the 11.0-ft wheel- base formerly assumed with a cab-over-engine wheelbase. Thus, tractors for double- and triple-trailer combination trucks with 28.5-ft trailers are still shorter than typical long-haul tractors but are longer than the tractors shown in the current edition of the Green Book. The front overhang for each tractor is based on a typical tractor from the field data that has the recommended wheelbase for that type of tractor. Figure 22 shows the three tractors recommended for use in the next edition of the Green Book, replacing the seven tractors shown in Figure 21. 5.5 Single-Trailer Combination Trucks The Green Book includes three design vehicles representing tractor-semitrailer combination trucks: • WB-40—Intermediate Semitrailer (see Figure 23) • WB-62—Interstate Semitrailer (see Figure 24) • WB-67—Interstate Semitrailer (see Figure 25) Each of these design vehicles consists of a truck tractor with a single semitrailer cargo unit attached with a kingpin connection. 5.5.1 WB-40 Intermediate Semitrailer The WB-40 design vehicle, shown in Figure 23, consists of a truck tractor pulling a single semitrailer cargo unit 33 ft in length. This design vehicle is shorter than most single-trailer combination trucks used today. The WB-40 design vehicle was recommended for retention in NCHRP Report 505 because the 33-ft trailer was found at that time to represent a common intermodal container size (Harwood et al. 2003).

48 Highway and Street Design Vehicles: An Update Figure 22. Dimensions of updated truck tractors for use with AASHTO design vehicles.

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 49 Source: AASHTO 2018. Figure 23. Dimensions of intermediate semitrailer truck design vehicle with a single 33-ft trailer (WB-40). Source: AASHTO 2018. Figure 24. Dimensions of interstate semitrailer truck design vehicle with a single 48-ft trailer (WB-62). Source: AASHTO 2018. Figure 25. Dimensions of interstate semitrailer truck design vehicle with a single 53-ft trailer (WB-67).

50 Highway and Street Design Vehicles: An Update 5.5.2 WB-62 Interstate Semitrailer The WB-62 design vehicle, shown in Figure 24, consists of a truck tractor pulling a single semi- trailer cargo unit 48 ft in length. This design vehicle represents a combination truck in common use. The 1982 STAA prohibited states from restricting the operation of single-trailer trucks with semitrailers up to 48 ft in length on the interstate system and the rest of the NN. Thus, this design vehicle can legally operate in every state. Furthermore, states were required to provide reasonable access for such trucks from the interstate system and the rest of the NN to services (locations providing food, fuel, and rest) and terminals (points of origin and destination for truck trips). 5.5.3 WB-67 Interstate Semitrailer The WB-67 design vehicle, shown in Figure 25, consists of a truck tractor pulling a single semitrailer cargo unit 53 ft in length. As documented in Section 5.5.4, this design vehicle also represents a combination truck in common use. 5.5.4 Existing Size Limits for Single-Trailer Combination Trucks Unlike truck combinations with multiple trailers (see Sections 5.6 and 5.7), there is no federal freeze on the maximum size of single-trailer trucks. Where states already allowed single-trailer combination trucks with trailers longer than 48 ft to operate, the 1982 STAA prohibited states from reducing that maximum trailer length. Table 24 shows the maximum trailer length grand- fathered by the 1982 STAA based on the laws and regulations in effect in each state before the passage of that legislation. The table shows that 17 states allowed single-trailer trucks with 53-ft trailers before 1982 and are, therefore, required by federal law to continue to allow com- bination trucks with 53-ft trailers on the interstate system and the rest of the NN. An additional 10 states are required by federal law to allow combination trucks longer than 53 ft on the interstate system and the rest of the NN. The grandfathered trailer lengths shown in Table 24 are minimum limits for the maximum lengths that states are required to allow on the interstate system and the rest of the NN. Nothing in federal law restricts states from allowing (or changing their regulations in the future to allow) trailers longer than these minimum lengths on the interstate system and the rest of the NN, or on any other road. All 50 states today allow combination trucks with 53-ft trailers to operate on at least some roads. Twenty-two states allow trucks with 53-ft trailers to operate only if the rear trailer axle(s) is pulled sufficiently forward to satisfy a specified KPRA distance criterion. Table 25 identifies these states. In 15 of the 22 states, the KPRA distance is measured from the kingpin to the center of the rear-axle group. In 7 of the 22 states, the KPRA distance is measured from the kingpin to the center of the rearmost axle. Since tandem axles are typically spaced with axle centers 4 ft apart, a maximum KPRA distance of 43 ft measured to the center of the rearmost axle of a tandem axle group is essentially equivalent to a 41-ft maximum KPRA distance measured to the center of the rear-axle group. The remaining 28 states not shown in Table 25 have no limitations on KPRA distance for semitrailers longer than 48 ft. The single-trailer combination truck with a 53-ft trailer (WB-67) is the largest single-trailer truck allowed to operate in most states and is so common that it should remain as a design vehicle. The single-trailer combination truck with a 48-ft trailer (WB-62) is an appropriate design vehicle because the 48-ft trailer length is explicitly specified in the 1982 STAA as a truck size that states must permit and because trucks with 53-ft trailers that operate under a 41-ft KPRA dis- tance limitation, with their rear axle (or axle group) moved forward to meet that KPRA distance

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 51 State/District Maximum semitrailerlengths on NN (ft-in.) Alabama 53-6 Alaska 48-0 Arizona 57-6 Arkansas 53-6 California 48-0 Colorado 57-4 Connecticut 48-0 Delaware 53-0 District of Columbia 48-0 Florida 48-0 Georgia 48-0 Hawaii 48-0 Idaho 48-0 Illinois 53-0 Indiana 48-6 Iowa 53-0 Kansas 57-6 Kentucky 53-0 Louisiana 59-6 Maine 48-0 Maryland 48-0 Massachusetts 48-0 Michigan 48-0 Minnesota 48-0 Mississippi 53-0 Missouri 53-0 Montana 53-0 Nebraska 53-0 Nevada 53-0 New Hampshire 48-0 New Jersey 48-0 New Mexico 57-6 New York 48-0 North Carolina 48-0 North Dakota 53-0 Ohio 53-0 Oklahoma 59-6 Oregon 53-0 Pennsylvania 53-0 Rhode Island 48-6 South Carolina 48-0 South Dakota 53-0 Tennessee 50-0 Texas 59-0 Utah 48-0 Vermont 48-0 Virginia 48-0 Washington 48-0 West Virginia 48-0 Wisconsin 48-0 Wyoming 57-4 Source: Appendix B to 23 CFR 658. Table 24. Grandfathered semitrailer lengths.

52 Highway and Street Design Vehicles: An Update limitation, have offtracking and swept path width that is essentially equivalent to that of the WB-62 design vehicle. For this reason, the WB-62 design vehicle is often used to represent 53-ft single-trailer trucks in states with KPRA distance limitations. Federal regulations based on the 1982 STAA prohibit states from restricting overall vehicle width on interstate highways and the rest of the NN to less than 8.5 ft. All the design vehicles for single-trailer combination trucks are 8.5 ft in width. The design vehicle drawings presented in Figures 23 through 25 show the trailers that transport cargo as enclosed vans. Other types of trailers include flatbeds, dump trucks (open at the top to transport solid commodities in bulk), enclosed tanks (to transport liquid commodities in bulk), and others. However, for consideration of geometric design issues related to offtracking and swept path width, it makes essentially no difference what trailer body type is used to transport cargo. The fifth-wheel positions for all combination trucks are assumed to be equivalent to the fifth- wheel positions in the current Green Book. 5.5.5 Recommended Design Vehicle Updates for Single-Trailer Combination Trucks—Intermediate Semitrailers As noted in Section 5.5.1, the intermediate semitrailer WB-40 design vehicle has been retained in the past, even though most single-trailer trucks are substantially larger, because its trailer represented the size of a common intermodal container. However, the current research has found that, in recent years, intermodal containers have increased in size. The current dimensions of intermodal containers used in worldwide commerce are summa- rized in Table 26. These data indicate that intermodal containers 40 ft in length now constitute 52% of the containers in use, representing 68% of total container capacity. These results indicate that the appropriate trailer length for a current intermediate semitrailer truck is 40 ft. State Maximum KPRA distance (ft) KPRA distance measured from kingpin to: Center-of-rear-axle group Center of rearmost axle Alaska 41.0 X California 40.0a X Connecticut 43.0 X Florida 41.0 X Illinois 45.5 X Indiana 43.0 X Maine 43.0 X Maryland 41.0 X Minnesota 43.0 X New Hampshire 41.0 X New Jersey 41.0 X New York 43.0 X North Carolina 41.0 X Pennsylvania 41.0 X Rhode Island 41.0 X South Carolina 41.0 X Tennessee 41.0 X Utah 41.0 X Vermont 41.0 X Virginia 41.0 X West Virginia 41.0 X Wisconsin 43.0 X a KPRA distance limited to 38 ft for semitrailers with a single rear axle. Table 25. States with KPRA distance limitations for single-trailer trucks with semitrailers longer than 48 ft.

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 53 Intermodal container type Percentage of worldwide intermodal container commerce Intermodal container outside dimensions (ft) By total number of container units By total container capacity Length Width Height 20-ft standard vans 24 16 20.0 8.0 8.5 40-ft standard vans 14 19 40.0 8.0 8.5 40-ft high-cube vansa 38 49 40.0 8.0 9.5 Othersb 24 16 Various 8.0 Various Source: Adapted from www.LSIU.co/resources-and-links/world-container-fleet, international standard ISO 668-2013(E), and data provided by the Port Authority of New York and New Jersey. a 40-ft high-cube van containers are 1 ft higher than standard van containers; they were first introduced in the late 1980s but have now become the predominant container size. b includes containers with a full range of widths shorter and longer than those shown. Table 26. Typical frequencies and sizes for intermodal containers. Figure 26. Dimensions of updated intermediate semitrailer truck design vehicle with a single 40-ft trailer (WB-47). The recommended dimensions for an intermediate semitrailer truck design vehicle (to be designated as the WB-47 design vehicle) are presented in Figure 26. This design vehicle has a trailer length of 40.0 ft, a wheelbase of 47.4 ft, and an overall length of 52.9 ft. The height and width of the intermediate semitrailer design vehicle remain unchanged. The appropriate tractor for this design vehicle is the typical city and short-haul tractor shown in Figure 22B. This design vehicle may be particularly appropriate for the design of port and intermodal terminal facilities. 5.5.6 Recommended Design Vehicle Updates for Single-Trailer Combination Trucks—Interstate Semitrailers Trailers with lengths of 53 ft, like the current WB-67 design vehicle, remain a very common trailer size for large single-trailer combination trucks operating on U.S. highways, as they can legally operate in all 50 states. Only a few states allow trucks with single semitrailers longer than 53 ft. Thus, retention of a design vehicle with a 53-ft trailer appears essential. Trailers with lengths of 48 ft, like the current WB-62 design vehicle, are not as common on U.S. roads as 53-ft trailers. However, there are two reasons why retention of a design vehicle with a single 48-ft semitrailer is appropriate. First, the 48-ft trailer length is specified in federal law, the 1982 STAA. Second, the wheelbase for a 48-ft single semitrailer truck is essentially equivalent to

54 Highway and Street Design Vehicles: An Update Figure 27. Dimensions of updated interstate semitrailer truck design vehicle with a single 48-ft trailer (WB-64). Figure 28. Dimensions of updated interstate semitrailer truck design vehicle with a single 53-ft trailer (WB-69). the wheelbase for a 53-ft semitrailer truck in a state with a maximum 41-ft kingpin-to-center-of- rear-axle-group limitation or a 43-ft kingpin-to-center-of-rearmost-axle limitation. Therefore, the design vehicle with a 48-ft single semitrailer may be useful in representing a 53-ft single semitrailer with the rear axles pulled forward to meet a state regulation. Table 24 shows that 17 states may find the 48-ft single semitrailer design vehicle useful. For these reasons, the 48-ft single semitrailer design vehicle should be retained. The trailer dimensions need not change for either the 48-ft or 53-ft single semitrailer design vehicles. However, in the next edition of the Green Book, both of these design vehicles should incorporate the revised long-haul tractor shown in Figure 22A. The height and width of these two design vehicles remain unchanged. With the revised tractor incorporated, the 48-ft and 53-ft single semitrailer design vehicles (to be designated as the WB-64 and WB-69 design vehicles) are shown in Figures 27 and 28, respectively.

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 55 5.6 Double-Trailer Combination Trucks The Green Book includes three design vehicles representing double-trailer combination trucks: • WB-67D—Double Bottom Semitrailer/Trailer (see Figure 29) • WB-92D—Rocky Mountain Double Semitrailer/Trailer (see Figure 30) • WB-109D—Turnpike Double Semitrailer/Trailer (see Figure 31) Each of these design vehicles consists of a truck tractor with a semitrailer cargo unit attached with a kingpin connection followed by a towed full-trailer cargo unit. 5.6.1 WB-67D Double Bottom or Twin-Trailer Truck The WB-67D design vehicle, shown in Figure 29, consists of a truck tractor pulling a semi- trailer cargo unit 28.5 ft in length followed by a full-trailer cargo unit 28.5 ft in length; truck combinations of this type are frequently referred to as twin-trailer trucks. The WB-67D rep- resents a truck that the 1982 STAA mandates all states must permit to operate on interstate highways and the rest of the NN. The 1982 STAA requires all states to allow double-trailer trucks with two 28-ft trailers to operate on the interstate system and the rest of the NN. The 1982 STAA Source: AASHTO 2018. Figure 29. Dimensions of double bottom or twin-trailer combination truck design vehicle with two 28.5-ft trailers (WB-67D). Source: AASHTO 2018. Figure 30. Dimensions of Rocky Mountain double design vehicle (WB-92D).

56 Highway and Street Design Vehicles: An Update also required states that previously allowed double-trailer trucks with two 28.5-ft trailers to continue to do so. This effectively established 28.5-ft trailer lengths as a minimum requirement for double-trailer trucks on the interstate system and the rest of the NN. Thus, the WB-67D has a strong basis in established law, as trucks of this type may operate in all 50 states. Furthermore, the WB-67D is likely to be needed as a standard design vehicle for the foreseeable future, since the 1991 ISTEA legislation (the “ISTEA freeze”) does not permit states to allow double-trailer trucks with trailer lengths greater than 28.5 ft to operate on the interstate system and the rest of the NN unless they were already allowed to operate before 1991. Because of the ISTEA freeze, allowing double-trailer trucks with trailers larger than the WB-67D’s to operate in additional places would require congressional legislation. Given federal legislation that has been in place since 1982 and 1991, most double-trailer trucks are limited to trailer lengths of 28.5 ft, so there is no need to change the trailer lengths in the current WB-67D design vehicle. However, a change in the design vehicle is needed to accom- modate a longer tractor, specifically the tractor shown in Figure 22C. Federal regulations based on the 1982 STAA prohibit states from restricting overall vehicle width on interstate highways and the rest of the NN to less than 8.5 ft. All the design vehicles for double-trailer combination trucks are 8.5 ft in width. 5.6.2 Double-Trailer Combination Design Vehicles Larger Than the WB-67D Table 27 summarizes the size and weight limits for double-trailer trucks in the 23 states that allow the operation of double-trailer trucks with trailer lengths that exceed 28.5 ft (i.e., larger than that of the WB-67D) as follows: • Maximum limits specified in state law for overall vehicle length, length of CC units, semi- trailer length, and full-trailer length. In most states, limits exist on only some, but not all, of these lengths. • Maximum limits on the weight on a single axle, a tandem axle, or on the GVW of the full vehicle. These weights include the combined weight of the vehicle itself and the cargo carried by the vehicle. In addition to the weights shown in the table, axle weights may be constrained by the federal bridge formula, a state bridge formula, maximum limits on weight per unit width of tires on a given axle, or state-specific tables of maximum axle or axle group weights. Source: AASHTO 2018. Figure 31. Dimensions of turnpike double design vehicle (WB-109D).

State Maximum vehicle length (ft) Maximum length (ft) for CC units Maximum semitrailer length (ft) Maximum full trailer length (ft) Maximum weight (lb) Comparison to dimensions of: Permitrequired? Roadway(s) included Access distance (mi) Minimum speed (mph) CommentsSingle axle Tandem axle Full vehicle (GVW) WB-92D WB-109D Alaska — 110 — — 20,000 38,000 (a) Longer Longer No Portions of SR 1, SR 2, and SR 3 5 (b) — Arizona — 95 — — 20,000 34,000 129,000 Longer Shorter Yes I-15; US 89 (within 20 mi of Utah); US 160/163 (Utah to New Mexico) 20 20 — Colorado — 111 — — 20,000 34,000 110,000 Longer Longer Yes Interstate system (except the mountainous portion of I-70) 10 20 Maximum weight subject to state and federal bridge formulas, whichever is least; must have 6 to 9 axles Florida — 106 — — (a) (a) 147,000 Longer Longer Yes Entire Florida's Turnpike except for the final connection to I-75 0 40(c) Staging areas provided at toll plazas; over 110,000 lb GVW must have tandem rear axles on tractor Hawaii — 65 — — (a) (a) (m) Shorter Shorter No All NN roads with one exception (d) — — Idaho — 95 — 20,000 34,000 105,500 Longer Shorter Yes All NN routes (e) — Maximum offtracking on 161-ft radius curve limited to 8.75 ft based on a formula Indiana — 106 — — 22,400 36,000 127,400(f) Longer Longer Yes(g) Entire Indiana Toll Road 15 45 Must have 5 to 9 axles Iowa (trucks to and from South Dakota) — 100 — — 20,000 34,000 129,000 Longer Similar Yes Commercial area around Sioux City (h) 40 Applies to trucks to and from South Dakota Iowa (trucks to and from Nebraska) — 65 — — 20,000 34,000 95,000 Shorter Shorter Commercial area around Sioux City (h) — Applies to trucks to and from Nebraska; doubles with CC length from 65 ft to 95 ft must travel empty Kansas — 109 — — 20,000 34,000 120,000 Longer Longer No Entire Kansas Turnpike 10(i) — Permit required for access beyond toll plazas Massachusetts — 104 — — 22,400 36,000 127,400 Longer Longer Yes Massachusetts Turnpike from New York to Exit 18 (Cambridge St.) 0 20 Staging areas provided at toll plazas. Specific maximum weights for tractors and trailers specified. Mississippi — 65 30 — 20,000 34,000 (a) Shorter Shorter No All NN roads (j) — Specific axle group weight limits apply Missouri (trucks to and from Kansas) 119 109 — — 20,000 34,000 120,000 Longer Longer Yes NN roads within 20 mi of Kansas, Nebraska, or Oklahoma state lines (k) — Same weight and vehicle dimensions as Kansas Turnpike Table 27. Legal double-trailer combination trucks with trailer lengths that exceed 28.5 ft by state. (continued on next page)

State Maximum vehicle length (ft) Maximum length (ft) for CC units Maximum semitrailer length (ft) Maximum full trailer length (ft) Maximum weight (lb) Comparison to dimensions of: Permitrequired? Roadway(s) included Access distance (mi) Minimum speed (mph) CommentsSingle axle Tandem axle Full vehicle (GVW) WB-92D WB-109D Missouri (trucks to and from Nebraska) — 65 48(l) 26-28(l) 20,000 34,000 95,000 Shorter unless empty Shorter Yes NN roads within 20 mi of Kansas, Nebraska, or Oklahoma state lines (k) 20 Same weight and vehicle dimensions as applicable in Nebraska. Maximum CC unit length is 95 ft for doubles traveling empty. Missouri (trucks to and from Oklahoma) — 110 — — 20,000 34,000 90,000 Longer Longer Yes NN roads within 20 mi of Kansas, Nebraska, or Oklahoma state lines (k) 20 Same weight and vehicle dimensions as applicable in Oklahoma Nebraska — 65 48(l) 26-28(l) 20,000 34,000 empty Similar Shorter Yes All NN roads (m) Not restricted — — Doubles with CC length from 65 ft to 95 ft must travel empty Nevada — 95 48 42(n) 20,000 34,000 129,000 Longer Shorter Yes All NN roads except on portion of US 93 Not restricted 20 New York — 102 — — 36,000 143,000(o) Longer Longer Yes Entire New York Thruway except for I-95 (d) 20 Specific axle group weight limits apply; over 110,000 lb GVW must have tandem rear axles on tractor North Dakota — 103 — — 20,000 34,000 105,500 Longer Longer Yes All NN roads 10 15 Specific axle group weight limits apply Ohio — 102 48 48 21,000 24,000-34,000 127,400(p) Longer Longer Yes Ohio Turnpike only 0 40 Staging areas provided at selected toll plazas; doubles must have 5 to 9 axles Oklahoma — 110 53 53 20,000 34,000 90,000 Longer Longer Yes Specified multilane divided highways 5(q) 40 Specific axle group weight limits apply Oregon — 68 40 35 20,000 34,000 105,500 Shorter Shorter Yes All NN roads (d) — Specific axle group weight limits apply South Dakota — 100 — — 20,000 34,000 129,000 Longer Similar Yes All interstate routes and selected additional NN routes (d) 40 Maximum offtracking on 161-ft radius curve limited to 8.75 ft based on formula Utah — 95 —— 20,000 34,000 129,000 Longer Shorter Yes All NN roads (d) 20 — Washington — 68 — — 20,000 34,000 105,500 Shorter Shorter Yes All NN roads except SR 123 and SR 410 in the vicinity of Mt. Rainier National Park All NN roads — — Wyoming — 81 48 40 20,000 36,000 117,000 Longer Shorter No All NN roads Not restricted — Tridem axle weight limited to 42.500 lb Source: Adapted from Appendix C to 23 CFR 658. (a) per values specified in state regulations for all trucks. (b) minimum engine power 400 hp. (c) minimum speed of 30 mph allowed on one 4-mi section. (d) as authorized by the state DOT. (e) access varies with computed offtracking. (f) allowable GVW varies with actual vehicle length. (g) permit required if over 90,000-lb GVW. (h) entire Sioux City commercial area. (i) 20-mi access distance at northeast end of turnpike (including travel to Missouri state line). (j) access permitted using all roads in the state. (k) all roads needed to reach terminals within 20 mi of the state line. (l) for doubles with CC lengths over 85 ft, trailers must be of approximately equal length. (m) doubles with CC length over 65 ft and limited to I-80 from Wyoming to Exit 440 (SR 50), with same access restrictions as triples. (n) if one trailer is 48 ft in length, the other trailer may not exceed 42 ft in length. (o) 142,000-lb GVW limit applies to 9-axle trucks; GVW limit for an 8-axle truck is 134,000 lb; B-train double limited to 127,000 lb; a B-train double (more common in Canada than in the United States) has fifth-wheel and kingpin connections between both the tractor and the first trailer and between the first trailer and the second trailer; thus, in a B-train double both trailers are semitrailers. (p) 90,000-lb GVW for doubles less than 90 ft in length. (q) 15-mi access distance allowed for two-lane roads that connect multilane divided highways. Table 27. (Continued).

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 59 • Comparisons of the maximum lengths to the dimensions of the AASHTO WB-92D and WB-109D design vehicles. The maximum vehicle length under state law is longer than, shorter than, or similar in length to the WB-92D or WB-109D. • An indication (yes or no) as to whether a permit from the state is needed for operation by maximum length vehicle. In many cases, the required permit is a “routine” or blanket permit, rather than a single-vehicle or single-trip permit. • A description of the specific roadways where the maximum length vehicle may operate. In various states, this ranges from a single road to all NN roads in the state. • The access distance from designated roadways that the trucks may travel to reach services (locations for food, fuel, or rest) or their origin or destination terminals. In some, states, specific access routes within the specified distance must be approved; in other states, any facility within the specified distance may be accessed. Where zero access distance is specified, staging areas are provided at entrances and exits from the designated roads where truck combinations may be made up and broken down. • The minimum speed that vehicles must be capable of maintaining either on specified grades or on any grade on which a specific vehicle will operate on a specific trip. The overall weight of the truck and the specified minimum speed govern the minimum engine horsepower needed for the truck tractor. • Comments that further explain the information in one or more of the table columns. The key length dimension used in the table to compare truck sizes is the maximum length of the CC units, or maximum CC length, defined as the distance from the front of the first trailer to the rear of the last trailer. For a double-trailer truck, the CC length is the sum of the two trailer lengths and the length of the space between the two trailers. The CC length for the WB-67D, shown in Figure 29, is 62 ft. The limits on maximum CC length for double-trailer trucks shown in Table 27 is as high as 111 ft. There are no federal rules that prohibit states from allowing the operation of double-trailer trucks larger than the WB-67D within a maximum GVW of 80,000 lb or less. However, very few states do this. In most cases, double-trailer trucks longer than the WB-67D that currently operate are authorized to operate with GVW that exceeds 80,000 lb. Trucks with two or more trailers operating with GVW over 80,000 lb are classified as longer combination vehicles (LCVs). The only LCVs allowed to operate on the NN are those that state and local laws and regulations in place before 1991 authorized; such LCVs authorized before 1991 are referred to as grandfathered truck configurations and the roads on which or the areas within which they operate are grandfathered locations. Thus, a freeze on LCV sizes and weights has existed since 1991, and exceptions to the freeze for truck configurations and locations not shown in Table 30 are possible only through legislation enacted by the U.S. Congress. The WB-92D and WB-109D design vehicles are intended to represent typical double-trailer trucks that states authorized to operate before the 1991 ISTEA freeze. The WB-92D design vehicle, illustrated in Figure 30, consists of a truck tractor pulling a semi- trailer cargo unit 48 ft in length followed by a full-trailer cargo unit 28.5 ft in length; truck com- binations of this type are frequently referred to as Rocky Mountain double combination trucks since they operate primarily in several western states. The CC length for the WB-92D design vehicle shown in Figure 30 is 80.5 ft. Table 27 shows that grandfathered state laws could allow Rocky Mountain double combination trucks to operate in 19 states: Alaska, Arizona, Colorado, Florida, Idaho, Indiana, Iowa, Kansas, Massachusetts, Missouri, Nebraska, Nevada, New York, North Dakota, Ohio, Oklahoma, South Dakota, Utah, and Wyoming. However, in 11 of these 19 states, the operation of Rocky Mountain doubles is limited to one road, very few roads, or a

60 Highway and Street Design Vehicles: An Update defined geographical area adjacent to the border of another state. It may be that Rocky Mountain double combinations, although legal, do not operate widely in these 11 states. For example, in Nebraska, vehicles with a CC length that exceeds 65 ft are allowed on most of I-80 but must travel empty, which limits their operation. The eight states where Rocky Mountain doubles can operate on a reasonably large network of roads are Colorado, Idaho, Nevada, North Dakota, Oklahoma, South Dakota, Utah, and Wyoming. Given the federal freeze on limits of state trailer lengths, states cannot change the trailer lengths for double-trailer trucks shown in Table 27. Therefore, there is no need to change the trailer lengths in the current WB-92D design vehicle. However, a change in the design vehicle is needed to accommodate a longer tractor, specifically the tractor shown in Figure 22C. The WB-109D design vehicle, illustrated in Figure 31, consists of a truck tractor pulling a semitrailer cargo unit 48 ft in length, which in turn tows a full-trailer cargo unit 48 ft in length. Truck combinations of this type are frequently referred to as turnpike double combination trucks because in several states they operate primarily on specific toll roads. The CC length for the WB-109D design vehicle shown in Figure 31 is 103 ft. Table 31 shows that grandfathered state laws allow turnpike double combination trucks to operate in 11 states: Alaska, Colorado, Florida, Indiana, Kansas, Massachusetts, Missouri, New York, North Dakota, Ohio, and Oklahoma. In 8 of these 11 states, the operation of turnpike doubles is limited to one road, very few roads, or a defined geographical area adjacent to the border of another state. The following toll roads allow the operation of turnpike doubles: • Florida’s Turnpike • Indiana Toll Road • Kansas Turnpike • Massachusetts Turnpike • New York State Thruway • Ohio Turnpike • Oklahoma Turnpikes The three states where turnpike doubles can operate on a reasonably large network of roads, rather than just a selected road or area, are Colorado, North Dakota, and Oklahoma. Trucks with CC lengths of 100 ft (approximately 2.5 ft shorter than the WB-109D’s) can operate in South Dakota and the adjacent area around Sioux City in Iowa. In six states, Alaska, Colorado, Florida, Indiana, Kansas, and Oklahoma, maximum CC lengths of 109 ft or more could permit the operation of turnpike doubles with two 53-ft trailers or with one 53-ft trailer and one 48-ft trailer. In Alaska, Florida, and Kansas, such operation is limited to a single road or very few roads. Given the federal freeze on state trailer length limits, states cannot change the trailer lengths for double-trailer trucks shown in Table 26. Therefore, there is no need to change the trailer lengths in the current WB-109D design vehicle. However, a change in the design vehicle is needed to accommodate a longer tractor, specifically the tractor shown in Figure 22A. 5.6.3 Updated Double-Trailer Combination Truck Design Vehicles Figures 32, 33, and 34 present the dimensions of the updated double-trailer truck design vehicles recommended in this research. These vehicles (to be designated as WB-71D, WB-96D, and WB-118D) replace the WB-67D, WB-92D, and WB-109D design vehicles, respectively. The pintle hook positions for the towbar connection for all full trailers are assumed to be at the rear of the preceding power unit or trailer. The height and width of these three design vehicles remain unchanged.

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 61 Figure 32. Dimensions of updated double bottom or twin-trailer combination truck design vehicle with two 28.5-ft trailers (WB-71D). Figure 33. Dimensions of updated Rocky Mountain double design vehicle (WB-96D). Figure 34. Dimensions of updated turnpike double design vehicle (WB-118D).

62 Highway and Street Design Vehicles: An Update 5.7 Triple-Trailer Combination Trucks The Green Book includes one design vehicle representing triple-trailer combination trucks: • WB-100T—Triple Semitrailer/Trailers (see Figure 35) The WB-100T design vehicle consists of a truck tractor pulling a semitrailer cargo unit 28.5 ft in length followed by two full-trailer cargo units each 28.5 ft in length. Truck combi- nations of this type are typically referred to as triple-trailer trucks. Unlike twin-trailer trucks equivalent to the WB-67D design vehicle, there is no mandate in the 1982 STAA or any other federal law that states must permit triple-trailer trucks to operate. Triple-trailer trucks that are allowed to operate at a maximum GVW over 80,000 lb are considered LCVs and are subject to the ISTEA freeze. Therefore, the only triple-trailer trucks that are allowed to operate on the interstate system and the rest of the NN are those that were allowed to operate under state law before 1991. Thus, neither new routes for triple-trailer truck operation nor larger triple- trailer trucks that are currently authorized on existing routes can operate without congres- sional legislation. Table 28 summarizes the size and weight limits for triple-trailer trucks in the 16 states that allow their operation. Table 28 includes the same information that was presented in Table 27 for double-trailer trucks, except that the length comparison shown in Table 28 is to the WB-100T design vehicle. The key length dimension used in the table to compare truck sizes is the maximum length of the CC units, or maximum CC length, defined as the distance from the front of the first trailer to the rear of the last trailer. For a triple-trailer truck, the CC length is the sum of the three trailer lengths and the lengths of the spaces between the first and second trailers and between the second and third trailers. The CC length for the WB-100T, shown in Figure 35, is 94.5 ft. The limits on maximum CC length for triple-trailer trucks shown in Table 28 are as high as 115.5 ft. Table 28 shows that grandfathered state laws allow triple-trailer combination trucks to operate in 16 states: Alaska, Arizona, Colorado, Idaho, Indiana, Iowa, Kansas, Missouri, Nebraska, Nevada, North Dakota, Ohio, Oklahoma, Oregon, South Dakota, and Utah. However, in 8 of these 16 states, the operation of triple-trailer trucks is limited to one road, very few roads, or a defined geographical area adjacent to the border of another state. In Nebraska, triple-trailer trucks are allowed on most of I-80 but must travel empty, which limits their operation. The eight Source: AASHTO 2018. Figure 35. Dimensions of triple semitrailer/trailer design vehicle (WB-100T).

State Maximum vehicle length (ft) Maximum length (ft) for CC units Maximum trailer length (ft) Maximum weight (lb) Comparison to WB-100T dimensions Permit required? Roadway(s) included Access distance (mi) Minimum speed (mph) CommentsSingle axle Tandem axle Full vehicle (GVW) Alaska — 110 28.5 20,000 38,000 (a) Longer Yes Portions of SR 1 and SR 3 5 (b) May 1 to Sept 30 only Arizona — 95 — 20,000 34,000 123,000(c) Similar Yes I-15; US 89 (within 20 mi of Utah); US 160/163 (Utah to New Mexico) 20 20 — Colorado — 115.5 — 20,000 34,000 110,000 Longer Yes Interstate system (except the mountainous portion of I-70) 10 20 Maximum weight subject to SBF and FBF, whichever is least Idaho — 95 — 20,000 34,000 105,500 Similar Yes All NN routes (d) Maximum offtracking on 161-ft radius curve limited to 8.75 ft based on a formula Indiana — 104.5 28.5 22,400 36,000 127,400(e) Longer Yes(f) Entire Indiana Toll Road 15 45 Maximum number of axes = 7 Iowa (trucks to and from South Dakota) — 100 — 20,000 34,000 129,000 Longer — Commercial area around Sioux City (g) 40 Applies to trucks to and from South Dakota Kansas 119 109 — 20,000 34,000 120,000 Longer No Entire Kansas Turnpike 10(h) — Permit required for access beyond toll plazas Kansas — 95 28.5 20,000 34,000 110,000 Similar Yes I-70 from Colorado to Exit 19 at Goodland, KS 10 20 — Missouri (trucks to and from Kansas) 119 109 28.5 20,000 34,000 120,000 Longer Yes NN roads within 20 mi of Kansas and Oklahoma state lines (i) — Same weight and vehicle dimensions as Kansas Turnpike Missouri (trucks to and from Oklahoma) — 95 29 20,000 34,000 90,000 Similar Yes NN roads within 20 mi of Kansas and Oklahoma state lines (i) 20 Same weight and vehicle dimensions as applicable in Oklahoma Nebraska 105 95 (j) Similar Yes I-80 from Wyoming to Exit 440 (SR 50) (k) — Only empty triples are allowed on I-80 in Nebraska Nevada — 95 — — — 20,000 34,000 129,000 Similar Yes All NN roads except on portion of US 93 (l) 20 — North Dakota — 103 — 20,000 34,000 105,500 Longer Yes All NN roads 10 15 — Ohio — 95 — 21,000 24,000-34,000 115,000 Similar Yes Ohio Turnpike only 0 40 Staging areas provided at toll plazas; only two minor exceptions (each 1 mi or less) to access route restriction; triples must have 7 to 9 axles Oklahoma — 95 29 20,000 34,000 90,000 Similar Yes Specified multilane divided highways 5(m) 40 Specific axle group weight limits apply Oregon 105 96 (j) 20,000 34,000 105,500 Similar Yes Most NN roads (l) — Specific axle group weight limits apply South Dakota — 100 — 20,000 34,000 129,000 Longer Yes All interstate routes and selected additional NN routes (l) 40 Maximum offtracking on 161-ft radius curve limited to 8.75 ft based on formula Utah — 95 — 20,000 34,000 129,000 Similar Yes All NN roads (l) 20 — Source: Adapted from Appendix C to 23 CFR 658. FBF = Federal bridge formula. SBF = State bridge formula. (a) per values specified in state regulations for all trucks. (b) minimum engine power 400 hp. (c) 129,000 lb on I-15. (d) access varies with computed offtracking. (e) allowable GVW varies with actual vehicle length. (f) permit required if over 90,000-lb GVW. (g) entire Sioux City commercial area. (h) 20-mi access distance at northeast end of turnpike (including travel to the Missouri state line). (i) all roads needed to reach terminals within 20 mi of the Kansas or Oklahoma state line. (j) trailers must be of approximately equal length. (k) access permitted only to staging areas with 6 mi of I-80; except for weather, emergency, and repair, triples cannot reenter the interstate after exiting. (l) as authorized by the state DOT. (m) 15-mi access distance allowed for two-lane roads that connect multilane divided highways. — Table 28. Legal triple-trailer combination trucks by state.

64 Highway and Street Design Vehicles: An Update states where triple-trailer trucks can operate on a reasonably large network of roads are Colorado, Idaho, Nevada, North Dakota, Oklahoma, Oregon, South Dakota, and Utah. Toll roads that allow the operation of triple-trailer trucks include the following: • Indiana Toll Road • Kansas Turnpike • Ohio Turnpike • Oklahoma Turnpikes The laws of six states permit the operation of triple-trailer trucks with trailers longer than 28.5 ft. These states are Colorado, Iowa, Kansas, Missouri, North Dakota, and South Dakota. In Iowa and Missouri, triple-trailer trucks only operate in limited geographical areas adjacent to the borders of other states. Kansas regulations permit triple-trailer trucks with CC lengths up to 109 ft to operate, but only on the Kansas Turnpike and adjacent access roads. More general operation of longer triple-trailer trucks is allowed in Colorado (up to 115.5-ft maximum CC length), North Dakota (up to 103-ft maximum CC length), and South Dakota (up to 100-ft maximum CC length). Federal regulations based on the 1982 STAA prohibit states from restricting overall vehicle width on interstate highways and the rest of the NN to less than 8.5 ft. The design vehicle for triple-trailer trucks is 8.5 ft in width. Since triple-trailer trucks with trailer lengths that exceed 28.5 ft operate in only six states, there does not appear to be a general need for a triple-trailer design vehicle with trailers longer than 28.5 ft. The change that appears needed for the WB-100T design vehicle is to use a larger cab-behind-engine tractor of the type shown in Figure 22C. The height and weight of the triple- trailer truck design vehicle remain unchanged. The updated triple-trailer design vehicle (to be designated as the WB-103T) is shown in Figure 36. 5.8 Intercity Buses and Motor Coaches Intercity buses and motor coaches are generally configured for long-distance, over-the-road transportation of passengers. However, similar bus configurations are also used within metro- politan areas for commuter transport, tour groups, and charter operations. In addition, one similar bus model is configured specifically for prisoner transportation. Figure 36. Dimensions of updated triple semitrailer/trailer design vehicle (WB-103T).

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 65 Source: AASHTO 2018. Figure 37. Dimensions for intercity bus (BUS-40) design vehicle. Source: AASHTO 2018. Figure 38. Dimensions for intercity bus (BUS-45) design vehicle. The Green Book includes two design vehicles representing intercity buses: • BUS-40—Intercity Bus (see Figure 37) • BUS-45—Intercity Bus (see Figure 38) The BUS-40 and BUS-45 design vehicles consist of three-axle buses with overall lengths of 40.5 ft and 45.5 ft and wheelbases of 25.3 ft and 28.5 ft, respectively. The BUS-40 and BUS-45 design vehicles both have overall widths of 8.5 ft and overall heights of 12.0 ft. Both design vehicles also incorporate an allowance of 3.5 ft for a bicycle rack with a three-bicycle capacity on the front of the vehicle in addition to the overall vehicle length. The research team has compiled a data set with dimensions of all intercity buses currently being manufactured and/or sold in the United States. This data set includes dimensions for 33 combinations of vehicle makes and models. These data were assembled from a variety of internet sites, including manufacturers’ data. Other bus configurations or variations of these standard configurations can likely be custom ordered, but these 33 models are representative of the vehicles being sold today. The 33 bus models for which data have been obtained include buses manufactured by BYD, Gillig, MCI, Prevost, Van Hool, and Volvo. There are nine models of two-axle buses and 24 models of three-axle buses. Three of these buses are double-decker models, and nine models are electric-powered. The conventional two-axle intercity buses can carry from 16 to 49 passengers, while the conventional three-axle intercity buses can carry from 47 to 70 passengers. The double- decker bus models can carry 77 to 98 passengers.

66 Highway and Street Design Vehicles: An Update Table 29 presents the data on the distribution of overall vehicle lengths for current model intercity buses, tabulated separately for two-axle and three-axle buses. The table shows that intercity buses currently on the market range in overall length from 23.50 ft to 45.80 ft. The BUS-40 design vehicle exceeds the length of all two-axle intercity buses and 16.7% of three-axle intercity buses. The BUS-45 design vehicle exceeds the length of all two-axle intercity buses and 62.5% of three-axle intercity buses. While 37.5% of three-axle buses exceed the length of the BUS-45 design vehicle, the maximum difference in length is only 0.80 ft (i.e., 45.80 ft versus 45.00 ft), or just over 9 in. Table 30 presents the data on the distribution of vehicle wheelbases for current model intercity buses, tabulated separately for two-axle and three-axle buses. The table shows that current inter- city buses range in wheelbase from 13.08 ft to 27.88 ft. The BUS-40 design vehicle exceeds the wheel- base of all two-axle intercity buses for which data are available and 29.2% of three-axle intercity buses. The BUS-45 design vehicle exceeds the wheelbase of all two- and three-axle intercity buses. Two-axle intercity buses currently being sold range in overall width (not including mirrors) from 6.76 ft to 8.50 ft. Three-axle intercity buses currently being sold range in overall width (not including mirrors) from 8.47 ft to 8.50 ft. Thus, all intercity buses currently being marketed have overall widths less than or equal to the BUS-40 and BUS-45 design vehicle width of 8.50 ft. It should also be noted that the 1982 STAA required states to allow vehicles with an overall width of 8.50 ft to operate on the interstate system and the rest of the NN, but no states allow vehicles wider than 8.5 ft to operate, except under permits. For intercity buses other than double-deckers, two-axle intercity buses currently being sold range in overall height from 9.00 ft to 11.73 ft, and three-axle intercity buses currently being sold range in overall height from 10.75 ft to 12.20 ft. Only 3 out of 30 buses, other than double- deckers, have heights greater than the 12.00-ft height of the BUS-40 and BUS-45 design vehicles: the Prevost H3-45 bus (with an overall height of 12.19 ft); the Van Hool TX-40 bus (12.21 ft); and the Van Hool TX-45 bus (12.21 ft). All three double-decker intercity bus models have heights over the 12.00-ft height of the BUS-40 and BUS-45 design vehicles. The heights of the double-decker buses include the two-axle BYD double-decker electric 35-ft bus (with an overall height of 13.08 ft); the three-axle Van Hool TX40 double-decker bus (13.35 ft); and the three-axle BYD double-decker electric 45-ft bus (13.35 ft). After a review of the available data, no change in the dimensions of the BUS-40 and BUS-45 design vehicles is recommended. The BUS-40 design vehicle appears to have an appropriate length for a bus smaller and shorter than the BUS-45 design vehicle. For the BUS-45 design vehicle, approximately 27% of intercity bus models have overall lengths that exceed the length of the BUS-45 design vehicle, but the maximum difference in overall length between the BUS-45 design vehicle and any currently marketed intercity bus model is 0.80 ft or just over 9 in. The 95th percentile bus length exceeds the current BUS-45 design vehicle length by only 0.59 ft, or about 7 in. In general, changes to design vehicle dimensions of 1 ft or less in overall length have not been recommended in this research. The overall width of the BUS-40 and BUS-45 design vehicles (8.50 ft) is appropriate because bus widths of 8.50 ft are allowed by federal and state regulations and no buses wider than 8.50 ft are currently marketed. The overall height of 12.00 ft for the BUS-40 and BUS-45 design vehicles appears to be appropriate. The maximum height for any intercity bus currently on the market is 12.20 ft and only 3 of 30 intercity bus models exceed 12.00 ft in height. Double-decker buses do not appear to be sufficiently common to constitute a design vehicle for nationwide application, although their overall height of 13.08 ft to 13.35 ft should be considered

Number of axles Number of models Vehicle length (ft) for specific intercity bus models Percent of intercity bus models with overall lengths exceeding the lengths of current design vehicles Minimum Mean 90th percentile 95th percentile Maximum BUS-40 BUS-45 All types combined 33 23.50 41.78 45.58 45.59 45.80 60.6 27.3 Two axles 9 23.50 34.46 40.50 40.50 40.50 0.0 0.0 Three axles 24 40.03 44.52 45.58 45.59 45.80 83.3 37.5 Vehicle length represents the length of the vehicle body (not including appurtenances such as bicycle racks). Table 29. Summary of overall vehicle lengths for all intercity bus models currently marketed in the United States. Number of axles Number of models Vehicle wheelbase (ft) for specific intercity bus models Percent of intercity bus models with wheelbases exceeding the lengths of current design vehicles Minimum Mean 90th percentile 95th percentile Maximum BUS-40 BUS-45 All types combined 29 13.08 24.18 27.88 27.88 27.88 58.6 0.0 Two axles 5 13.08 18.34 20.87 20.87 20.87 0.0 0.0 Three axles 24 19.62 25.39 27.88 27.88 27.88 70.8 0.0 Wheelbase data are not available for four of the nine two-axle intercity buses. Table 30. Summary of vehicle wheelbases for all intercity bus models currently marketed in the United States.

68 Highway and Street Design Vehicles: An Update in areas where they operate. A note will be included with the discussion of the bus design vehicles that vehicle heights up to 13.5 ft may need to be considered to accommodate double-decker buses. It should be noted that many of the truck design vehicles in the Green Book already have an overall height of 13.5 ft. The Green Book sets a minimum vertical clearance for over- head structures of at least 14 ft, which can accommodate current double-decker buses. 5.9 School Buses School buses are generally configured for transporting students from home to school and back, generally over short to medium distances. Similar bus configurations (often used school buses) are used for church and camp transportation or short-distance charters. The Green Book includes two design vehicles representing school buses: • S-BUS-36—Conventional School Bus (65 passengers) (see Figure 39) • S-BUS-40—Large School Bus (84 passengers) (see Figure 40) The S-BUS-36 and S-BUS-40 design vehicles consist of two-axle buses with overall lengths of 35.8 ft and 40.0 ft and wheelbases of 21.3 ft and 20.0 ft, respectively. The wheelbases for the S-BUS-36 and S-BUS-40 design vehicles appear inconsistent at first glance, with a longer Source: AASHTO 2018. Figure 39. Dimensions for conventional school bus (65-passenger) (S-BUS-36) design vehicle. Source: AASHTO 2018. Figure 40. Dimensions for large school bus (84-passenger) (S-BUS-40) design vehicle.

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 69 wheelbase shown in the Green Book for the shorter of the two design vehicles. However, this appears to result from the different relative positions of the front door and the front axle in the S-BUS-36 and S-BUS-40 design vehicles. The S-BUS-36 and S-BUS-40 design vehicles both have overall widths of 8.0 ft and overall heights of 10.5 ft. School buses are classified into four types (A, B, C, and D), as illustrated in Figure 41. Only Type C and Type D are sufficiently large that they might be appropriate as design vehicles, so the following discussion focuses on those types. The Government Accountability Office (GAO) indicates, based on industry sources, that Type C school buses (see typical drawing in Figure 39) constituted 70% of school bus sales in 2014 (GAO 2017). The research team has compiled a data set with dimensions of school buses currently being manufactured and/or sold in the United States. This data collection activity identified 170 school bus makes and models currently marketed in the United States, including small variations among similar models with different fuel types [e.g., buses powered by gasoline, diesel, compressed natural gas (CNG), and electric batteries]. Table 31 presents the data on the distribution of vehicle wheelbases for current model school buses, tabulated separately for Type C and Type D school buses. The table shows that current school buses range in wheelbase from 11.33 ft to 25.25 ft. National specifications for school buses limit the overall bus width to 8.5 ft, excluding acces- sories, such as mirrors (16th National Congress on School Transportation 2015). This maximum limit exceeds the 8.0-ft width of both Green Book design vehicles. However, no Types C or D school Source: Government Accountability Office 2017. Figure 41. Types of school buses. Table 31. Summary of vehicle wheelbases for all Type C and Type D school bus models currently marketed in the United States. School bus type Number of models Vehicle wheelbase (ft) for specific school bus models Percent of school bus models with wheelbases exceeding the wheelbases of current design vehicles Minimum Mean 90th percentile 95th percentile Maximum Types C and D combined 76 11.33 18.90 23.08 23.33 25.25 Type C 43 13.17 19.20 23.25 23.33 23.33 Type D 33 11.33 18.51 23.00 23.08 25.25 S-BUS-36 28.6 30.2 2.9 S-BUS-40 40.3 41.9 35.2

70 Highway and Street Design Vehicles: An Update Figure 42. Dimensions for updated conventional school bus (65-passenger) (S-BUS-38) design vehicle. buses marketed in the United States were found on the internet with widths greater than the 8.0-ft width of the current S-BUS-36 and S-BUS-40 design vehicles. All Type C and Type D school buses marketed in the United States were found to have heights ranging from 10.17 ft to 10.67 ft (i.e., slightly less to slightly more than the 10.5-ft height of the S-BUS-36 and S-BUS-40 design vehicles). The wheelbase and overall length for the updated school bus design vehicles were selected based on data from manufacturers’ specifications. The front and rear overhangs were selected to match the difference between the overall length and wheelbase. Based on the available data, it appears that the wheelbase of the Type C school bus design vehicle (currently designated as the S-BUS-36 design vehicle) should be increased by 2 ft from 21.3 ft to 23.3 ft, which represents the 90th and 95th percentiles, respectively, of Type C buses currently being marketed. The overall length of this design vehicle would be increased from 35.8 ft to 37.8 ft, and the updated design vehicle would be designated as the S-BUS-38 design vehicle. Note that the Type C design vehicle constitutes 70% of school bus sales. The Type D school bus design vehicle (currently designated as the S-BUS-40) should have a longer wheelbase because 35.2% of Type D bus models exceed the current wheelbase of 20.0 ft. However, vehicle dimension data do not support the long rear overhang of 13.0 ft for this design vehicle. The appropriate dimensions appear to be a front overhang of 7.0 ft, a wheelbase of 25.0 ft, and a rear overhang of 8.0 ft, with the same overall length of 40.0 ft as the current design vehicle. Thus, even with revised dimensions, this design vehicle would keep the current desig- nation of S-BUS-40. The overall width of the S-BUS-38 and S-BUS-40 design vehicles would remain 8.0 ft. The overall height of the S-BUS-38 and S-BUS-40 design vehicles would be increased to 10.67 ft to match the tallest school buses currently being marketed. The updated S-BUS-38 and S-BUS-40 design vehicles are shown in Figures 42 and 43, respec- tively. The recommended S-BUS-40 design vehicle is the same length as the CITY-BUS design vehicle discussed in Section 5.10, although it is 0.5 ft narrower in width. 5.10 Transit Buses Transit buses are generally configured for transporting passengers in urban areas with frequent bus stops at which passengers board and leave the bus. The Green Book includes two design vehicles representing transit buses: • CITY-BUS—City Transit Bus (see Figure 44) • A-BUS—Articulated Bus (see Figure 45)

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 71 Figure 43. Dimensions for updated large school bus (84-passenger) (S-BUS-40) design vehicle. Figure 44. Dimensions for city transit bus (CITY-BUS) design vehicle. Source: AASHTO 2018. Figure 45. Dimensions for articulated bus (A-BUS) design vehicle.

72 Highway and Street Design Vehicles: An Update Table 32. Total vehicle length for transit buses. Transit bus Number of models Vehicle length (ft) Percent of transit buses exceeding the length of current design vehicles Minimum Mean 90th percentile 95th percentile Maximum City bus 18 29.0 36.4 40.1 40.3 41.0 11.1 Articulated bus 3 60.7 61.2 61.8 61.9 62.0 100.0 Figure 46. Dimensions for updated articulated bus (A-BUS) design vehicle. The CITY-BUS design vehicle, shown in Figure 44, is a two-axle single-unit bus with an overall length of 40.0 ft and a wheelbase of 25.0 ft. The CITY-BUS design vehicle incorporates a 3.5-ft bicycle rack on the front of the vehicle. The CITY-BUS design vehicle has a height of 10.5 ft and a width of 8.5 ft, not including mirrors. The A-BUS design vehicle, shown in Figure 45, is a three-axle bus with an overall length of 60.0 ft and wheelbases of 22.0 ft and 19.4 ft. The front portion of the A-BUS design vehicle is 36.8 ft in length. The rear portion of the A-BUS—which can pivot around a fixed point on the front portion of the vehicle and, therefore, functions as a semitrailer—is 23.2 ft in length. The front portion of an articulated bus is typically, but not always, the power unit. The A-BUS design vehicle has a height of 11.0 ft and a width of 8.5 ft, not including mirrors. The presence of the articulation point reduces the turning radius of the A-BUS; the Green Book indicates that the 60-ft A-BUS design vehicle can turn in a tighter radius than the 40-ft CITY-BUS design vehicle since the A-BUS design vehicle is articulated. Table 32 presents a summary of the total lengths of transit buses. Length descriptive statistics are shown for both city buses and articulated buses. These data are based on vehicle dimension data found on manufacturers’ websites. Table 32 shows that only 11% of city transit buses currently on the market exceed the length of the CITY-BUS design vehicle. The maximum length of city transit buses on the market is 41.0 ft, or 1.0 ft longer than the CITY-BUS design vehicle. No change in dimensions of the CITY-BUS design vehicle is recommended since it is within 1.0 ft of the longest similar vehicle on the market. Table 32 shows that all three articulated buses currently on the market are longer than the 60-ft A-BUS design vehicle, by a maximum of 2.0 ft. It does, therefore, appear appropriate to increase the overall length of the A-BUS design vehicle by 2.0 ft. Figure 46 shows the dimensions of the updated A-BUS design vehicle. The height and width of the CITY-BUS and A-BUS design vehicles remain unchanged. Other types of transit buses, such as double-decker buses, do not appear to be used in suf- ficient numbers to be considered as a design vehicle.

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 73 Source: AASHTO 2018. Figure 48. Dimensions for car and camper trailer (P/T) design vehicle. Source: AASHTO 2018. Figure 47. Dimensions for motor home (MH) design vehicle. 5.11 Recreational Vehicles RVs are single-unit vehicles or vehicles pulling trailers with a specific recreational purpose— camping or transporting recreational equipment such as a boat. The Green Book includes four design vehicles representing RVs: • MH—Motor Home (see Figure 47) • P/T—Car and Camper Trailer (see Figure 48) • P/B—Car and Boat Trailer (see Figure 49) • MH/B—Motor Home and Boat Trailer (see Figure 50) The MH design vehicle, shown in Figure 47, is a two-axle single-unit vehicle with an overall length of 30.0 ft and a wheelbase of 20.0 ft. The MH design vehicle has a height of 12.0 ft and a width of 8.0 ft. The P/T design vehicle, shown in Figure 48, is a combination of the P design vehicle and a two-axle enclosed trailer, referred to in the current Green Book as a camper trailer. This trailer is more appropriately termed a travel trailer. The P/T design vehicle has an overall length of 48.7 ft, a height of 10.0 ft, and a width of 8.0 ft. The dimensions of the passenger car are the same as shown for the P design vehicle in Table 1 and Figure 15. The camper trailer is a semitrailer with a length of 29.7 ft from the rear of the passenger car to the rear of the camper body.

74 Highway and Street Design Vehicles: An Update The P/B design vehicle, shown in Figure 49, is a combination of the P design vehicle and a single-axle boat trailer with a boat in place on the trailer. The P/B design vehicle has an overall length of 42.0 ft and a width of 8.0 ft. No height is specified for this design vehicle. The dimen- sions of the passenger car are the same as shown for the P design vehicle in Table 1 and Figure 15. The boat trailer is a semitrailer with a length of 23.0 ft from the rear of the passenger car to the rear of the boat being carried by the trailer. The MH/B design vehicle, shown in Figure 50, is a combination of the MH design vehicle and the same single-axle boat trailer with a boat in place considered for the P/B design vehicle. The MH/B design vehicle has an overall length of 53.0 ft, a height of 12.0 ft, and a width of 8.0 ft. The dimensions of the motor home are the same as shown for the MH design vehicle in Table 1 and Figure 47. The boat trailer is a semitrailer with a length of 23.0 ft from the rear of the motor home to the rear of the boat being carried by the trailer, identical to the boat trailer shown in Figure 49. Data on dimensions of RVs that were on the market as of 2019 were obtained by compiling data available online from manufacturers. 5.11.1 Recommended Update for Motor Home Design Vehicle Motor homes are self-propelled single-unit vehicles with living and sleeping spaces that may or may not be integrated with the driver’s compartment. Motor homes are classified into three classes: • Class A motor homes are the largest size of motor home and are typically constructed on a truck chassis or commercial bus chassis. The MH design vehicle shown in Figure 47 is a Class A motor home. Source: AASHTO 2018. Figure 49. Dimensions for car and boat trailer (P/B) design vehicle. Source: AASHTO 2018. Figure 50. Dimensions for motor home and boat trailer (MH/B) design vehicle.

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 75 • Class B motor homes are typically built on the chassis of a conventional van and are sometimes referred to as a campervan. • Class C motor homes are typically built on a pickup truck platform with an extended chassis to support the motor home. Class C motor homes often have a sleeping area in an alcove that extends over the driver’s compartment. Figure 51 illustrates these three types of motor homes. Class A Motor home Class B Motor home Class C Motor home Figure 51. Examples of motor home Classes A, B, and C.

76 Highway and Street Design Vehicles: An Update Motor home class Number of models Vehicle length (ft) for motor home classes Percentage of models longer than the MH design vehicleMinimum Mean 90th percentile 95th percentile Maximum Class A 134 28.42 37.33 43.75 44.96 44.96 94.0 Class B 21 19.42 22.63 24.75 24.75 24.75 0.0 Class C 130 22.08 28.20 32.50 38.69 40.17 36.2 Table 33. Distribution of vehicle lengths for motor homes by class. Motor home class Number of models Wheelbase (ft) for motor home classes Percentage of models with wheelbases longer than the MH design vehicle Minimum Mean 90th percentile 95th percentile Maximum Class A 136 14.83 20.03 24.70 25.25 26.00 56.0 Class B 21 12.00 13.45 14.17 14.17 14.17 0.0 Class C 108 13.00 15.90 18.58 23.25 25.75 5.4 Table 34. Distribution of wheelbases for motor homes by class. Figure 52. Dimensions for updated motor home (MH) design vehicle. Tables 33 and 34 present descriptive statistics for vehicle lengths and wheelbases, respectively, of the three motor home classes. The data in Tables 33 and 34 indicate that Class A motor homes have the largest lengths and wheelbases and would have the greatest offtracking and swept path width for any of the motor home classes. Thus, it is appropriate that the MH design vehicle represents a Class A motor home. The tables show that 94% of Class A motor homes currently on the market exceed the length of the MH design vehicle, and 56% of Class A motor homes currently on the market exceed the wheelbase of the MH design vehicle. Thus, it appears the overall length and wheelbase of the MH design vehicle should be increased. Table 33 indicates that a motor home with an overall length of 44 ft would fall between the 90th and 95th percentile of motor home lengths. Figure 52 shows an updated motor home design vehicle with an overall length of 44 ft. Classes B and C motor homes would generally experience less offtracking and swept path width than a Class A motor home. Thus, it is reasonable that there are no separate design vehicles for Classes B or C motor homes. A Class B motor home is essentially a van and would have offtracking and swept path width very similar to the P and PU design vehicles. A Class C motor home is essentially a slightly elongated pickup truck and could be represented by the PU design vehicle recommended in Section 5.2.

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 77 Trailer type Number of models Length (ft) for recreational trailers Percentage of models longer than the P/T design vehicle trailer Minimum Mean 90th percentile 95th percentile Maximum Travel trailer 1,540 10.00 30.05 38.92 40.92 45.42 55.8 Table 35. Distribution of trailer lengths for recreational trailers. Figure 53. Dimensions for updated pickup truck and travel trailer (PU/T) design vehicle. 5.11.2 Recommended Update for RV Design Vehicle with a Travel Trailer Manufacturers’ data on trailer dimensions were also collected for travel trailers used in RVs. These dimensions are summarized in Table 35. Travel trailers are living units pulled by passenger vehicles. Table 35 presents summary statistics for the length of travel trailers, including popup campers. Lengths range from 10 ft to over 45 ft. The table shows that almost 56% of travel trailers on the market today exceed the 27-ft length of the camper trailer for the P/T design vehicle shown in Figure 48. This suggests the need to increase the trailer length for the P/T design vehicle. Table 35 and the field data described in Section 4.3 suggest an appropriate overall travel trailer length of 36 ft. Based on field observations, confirmed by the responses to the survey reported in Chapter 3, it appears that in today’s fleet, a pickup truck is a more likely vehicle than a passenger car to be pulling a travel trailer. Thus, the updated travel trailer design vehicle, incorporating the PU design vehicle as the power unit, is shown in Figure 53. This updated recreational vehicle, including a travel trailer, is designated as the PU/T design vehicle. 5.11.3 Recommended Update for RV Design Vehicles with a Boat Trailer No data on the sizes of current boat trailers were found in internet searches. However, the boat trailer included in the current P/B and MH/B design vehicles appears to be a rea- sonable choice for continued usage. For the same reasons cited for the travel trailer design vehicle, it appears appropriate for the P/B design vehicle to incorporate a pickup truck rather than a passenger car as the power unit. An updated pickup truck and boat design vehicle is presented in Figure 54.

78 Highway and Street Design Vehicles: An Update Figure 54. Dimensions for updated pickup truck and boat trailer (PU/B) design vehicle. Figure 55. Dimensions for updated motor home and boat trailer (MH/B) design vehicle. An updated motor home and boat trailer (MH/B) design vehicle, illustrated in Figure 55, combines the MH design vehicle and the same boat trailer used in the updated PU/B design vehicle. The height and width of all four recreational design vehicles remain unchanged. 5.12 Other Vehicle Configurations for Potential Consideration as Design Vehicles Four additional vehicle configurations were considered in the research as potential design vehicles: truck-trailer combinations, automobile transporters, fire engines, and garbage trucks. Truck-trailer combinations and automobile transporters do not appear to be present in the traffic stream with sufficient frequency to be considered as design vehicles. Fire engines and garbage trucks are key issues in road design because these vehicle types travel essentially everywhere on the road system. Chapter 6 documents that road design for these vehicle types can be addressed through consideration of other design vehicles. Consideration has also been given to road design for vehicles with low ground clearance. This issue is addressed in Chapter 7. 5.13 Summary of Updated Design Vehicle Dimensions In summary, the research team has made the following recommendations for consideration by AASHTO for the design vehicles in the Green Book:

Updated Dimensions and Recommended Additions to the Green Book Design Vehicles 79 • One new design vehicle, a pickup truck (PU) should be added. • Four design vehicles should remain unchanged: – Three-axle single-unit truck (SU-40) – Intercity bus (BUS-40) – Intercity bus (BUS-45) – City transit bus (CITY-BUS) • The remaining 16 design vehicles should incorporate revised dimensions. The symbols for most of these design vehicles have changed to reflect their revised dimensions. Table 36 summarizes the recommended changes in Green Book design vehicles. Table 37 shows the updated vehicle dimensions for the 21 potential design vehicles recommended in this chapter in the format that will be used in the updated Green Book. (continued on next page) Table 36. Summary of recommended design vehicle revisions. Vehicle description Current symbola Revised symbolb Recommended changes in design vehicle dimensions Passenger vehicles Passenger car P P Length reduced from 19.0 ft to 16.8 ft Wheelbase reduced from 11.0 ft to 9.8 ft Rear overhang reduced from 5.0 ft to 4.0 ft No other changes in dimensions Pickup truck — PU New design vehicle with: Length 20.3 ft Wheelbase 13.0 ft Front overhang 3.2 ft Rear overhang 4.1 ft Single-unit trucks Two-axle single-unit truck SU-30 SU-33 Length increased from 30.0 ft to 33.0 ft Wheelbase increased from 20.0 ft to 23.0 ft No other changes in dimensions Three-axle single-unit truck SU-40 SU-40 No changes in dimensions Single-trailer combination trucks Intermediate semitrailer WB-40 WB-47 Length increased from 45.4 ft to 52.9 ft Trailer length increased from 33.0 ft to 40.0 ft Wheelbase increased from 25.5 ft to 32.5 ft Tractor wheelbase increased from 12.5 ft to 12.9 ft Interstate semitrailer WB-62 WB-64 Length increased from 69.0 ft to 70.0 ft Tractor wheelbase increased from 19.5 ft to 21.0 ft Tractor front overhang decreased from 4.0 ft to 3.5 ft No other changes in dimensions WB-67 WB-69 Length increased from 73.5 ft to 74.5 ft Tractor wheelbase increased from 19.5 ft to 21.0 ft Tractor front overhang decreased from 4.0 ft to 3.5 ft No other changes in dimensions Double-trailer combination trucks Double bottom or twin-trailer semitrailer/full trailer WB-67D WB-71D Length increased from 72.3 ft to 77.5 ft Tractor wheelbase increased from 11.0 ft to 15.0 ft Tractor front overhang increased from 2.3 ft to 3.5 ft No other changes in dimensions Rocky Mountain double semitrailer/full trailer WB-92D WB-96D Length increased from 97.3 ft to 102.0 ft Tractor wheelbase increased from 17.5 ft to 18.9 ft Tractor front overhang increased from 2.3 ft to 3.5 ft No other changes in dimensions Turnpike double semitrailer/full trailer WB-109D WB-118D Length increased from 114.0 ft to 124.0 ft Tractor wheelbase increased from 12.2 ft to 18.9 ft Tractor front overhang increased from 2.3 ft to 3.5 ft No other changes in dimensions

80 Highway and Street Design Vehicles: An Update Table 36. (Continued). Vehicle description Current symbola Revised symbolb Recommended changes in design vehicle dimensions Recreational vehicles Motor home MH MH Length increased from 30.0 ft to 44.0 ft Wheelbase increased from 20.0 ft to 26.0 ft Front overhang increased from 4.0 ft to 6.0 ft Rear overhang increased from 6.0 ft to 12.0 ft No other changes in dimensions Pickup truck with travel trailer P/T PU/T PU design vehicle substituted for P design vehicle as towing vehicle Distance from trailer hitch to rear axles increased from 17.7 ft to 24 ft Rear overhang increased from 12.0 ft to 14.0 ft No other changes in dimensions Pickup truck with boat trailer P/B PU/B PU design vehicle substituted for P design vehicle as towing vehicle No other changes in dimensions Motor home with boat trailer MH/B MH/B Revised MH design vehicle substituted for current MH design vehicle as towing vehicle No other changes in dimensions a Symbol used in the current Green Book (AASHTO 2018). b Symbol recommended for use in the next edition of the Green Book. School buses School bus (65 passengers) S-BUS-36 S-BUS-38 Length increased from 35.8 ft to 37.8 ft Wheelbase increased from 21.3 ft to 23.3 ft Front overhang increased from 2.5 ft to 3.8 ft Rear overhang decreased from 12.0 ft to 10.7 ft No other changes in dimensions School bus (84 passengers) S-BUS-40 S-BUS-40 Wheelbase increased from 20.0 ft to 25.0 Rear overhang decreased from 13.0 ft to 8.0 ft No other changes in dimensions Transit buses City transit bus CITY-BUS CITY-BUS No changes in dimensions Articulated bus A-BUS A-BUS Length increased from 60.0 ft to 62.0 ft Power unit wheelbase increased from 22.0 ft to 24.0 ft No other changes in dimensions Triple-trailer combination trucks Triple semitrailer/full trailer/full trailer WB-100T WB-103T Length increased from 104.8 ft to 110.0 ft Tractor wheelbase increased from 11.0 ft to 15.0 ft Tractor front overhang increased from 2.3 ft to 3.5 ft No other changes in dimensions Intercity buses Intercity buses (motor coaches) BUS-40 BUS-40 No changes in dimensionsBUS-45 BUS-45 No changes in dimensions

Design vehicle type Symbol Dimensions (ft) Overall Overhang WB1 WB2 S T WB3 WB4 Typical kingpin-to- center-of-rear tandem axleHeight Width Length Front Rear Passenger car P 5.5 7.0 16.8 3.0 4.0 9.8 — — — — — — Pickup truck PU 6.5 7.0 20.3 3.2 4.1 13.0 Single-unit truck (two-axle) SU-30 11.0–13.5 8.0 30.0 4.0 6.0 20.0 — — — — — — Single-unit truck (three-axle) SU-40 11.0–13.5 8.0 39.5 4.0 10.5 25.0 — — — — — — Buses Intercity bus (motor coaches) BUS-40 12.0 8.5 40.5 6.3 9.0 a 25.3 — — — — — — BUS-45 12.0 8.5 45.5 6.2 9.0a 28.5 — — — — — — City transit bus CITY-BUS 10.5 8.5 40.0 7.0 8.0 25.0 — — — — — — Conventional school bus (65 passengers) S-BUS-38 10.5 8.0 37.8 3.8 10.7 23.3 — — — — — — Large school bus (84 passengers) S-BUS-40 10.5 8.0 40.0 7.0 8.0 25.0 — — — — — — Articulated bus A-BUS 11.0 8.5 62.0 8.6 10.0 24.0 19.4 6.2b 13.2b — — — Combination trucks Intermediate semitrailer WB-47 13.5 8.0 52.9 3.0 4.5a 12.9 32.7 — — — — 32.7 Interstate semitrailer WB-64* 13.5 8.5 70.0 3.5 4.5a 21.0 41.9 — — — — 41.9 Interstate semitrailer WB-69** 13.5 8.5 74.5 3.5 4.5a 21.0 45.5 — — — — 45.5 Double bottom semitrailer/trailer WB-71D 13.5 8.5 77.5 3.5 3.0 15.0 23.0 3.0c 7.0c 23.0 — 23.0 Rocky Mountain double semitrailer/trailer WB-96D 13.5 8.5 102.0 3.5 3.0 21.0 40.5 4.5 7.0 23.0 — 40.5 Triple semitrailer/trailers WB-103T 13.5 8.5 109.0 3.5 3.0 15.0 23.0 3.0d 7.0d 23.0 23.0 23.0 Turnpike double semitrailer/trailer WB-118D* 13.5 8.5 124.0 3.5 4.5a 21.0 40.5 4.5e 10.0e 40.5 — 40.5 Recreational vehicles Motor home MH 12.0 8.0 44.0 6.0 12.0 26.0 — — — — — — Pickup truck and travel trailer PU/T 10.0 8.0 59.1 3.2 14.0 13.0 — 4.1 24.0 — — — Pickup truck and boat trailer PU/B — 8.0 43.3 3.2 8.0 13.0 — 4.1 15.0 — — — Motor home and boat trailer MH/B 12.0 8.0 67.0 6.0 8.0 26.0 — 12.0 15.0 — — — * Design vehicle with 48.0-ft trailer as adopted in the 1982 Surface Transportation Assistance Act (STAA). ** Design vehicle with 53.0-ft trailer as grandfathered in with the 1982 Surface Transportation Assistance Act (STAA). a This is the length of the overhang from the center of the tandem axle assembly. b Combined dimension is 19.4 ft and articulating section is 4.0 ft wide. c Combined dimension is typically 10.0 ft. d Combined dimension is typically 10.0 ft. e Combined dimension is typically 14.5 ft. WB1, WB2, WB3, and WB4 are the effective vehicle wheelbases, or distances between axle groups, starting at the front and working toward the back of each unit. S is the distance from the rear effective axle to the hitch point or point of articulation. T is the distance from the hitch point or point of articulation measured back to the center of the next axle or the center of the tandem axle assembly. Table 37. Updated design vehicle dimensions.

Next: Chapter 6 - Turning Performance of Updated Design Vehicles »
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 Highway and Street Design Vehicles: An Update
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Approximately 55 percent of the passenger vehicles registered in the United States are light trucks, such as sport utility vehicles, vans, minivans, and pickup trucks. Conventional automobiles, such as sedans and coupes, make up the rest of passenger vehicles.

NCHRP Research Report 1061: Highway and Street Design Vehicles: An Update, from TRB's National Cooperative Highway Research Program, proposes revisions to the dimensions of 16 of the 20 design vehicles used in the 2018 edition of AASHTO’s A Policy on Geometric Design of Highways and Streets, commonly known as the Green Book.

Supplemental to the report is a spreadsheet tool.

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