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Highway and Street Design Vehicles: An Update (2023)

Chapter: Chapter 4 - Assembly of Data on the Current Vehicle Fleet

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Suggested Citation:"Chapter 4 - Assembly of Data on the Current Vehicle Fleet." 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 4 - Assembly of Data on the Current Vehicle Fleet." 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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Page 32
Page 33
Suggested Citation:"Chapter 4 - Assembly of Data on the Current Vehicle Fleet." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
Page 33
Page 34
Suggested Citation:"Chapter 4 - Assembly of Data on the Current Vehicle Fleet." National Research Council. 2023. Highway and Street Design Vehicles: An Update. Washington, DC: The National Academies Press. doi: 10.17226/27236.
×
Page 34
Page 35
Suggested Citation:"Chapter 4 - Assembly of Data on the Current Vehicle Fleet." 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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Page 35

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31   This chapter describes the assembly of data on the U.S. vehicle fleet as part of this research. 4.1 Vehicle Registration Data/Fleet Composition for Major Vehicle Types Table 17 presents a summary of the U.S. vehicle fleet based on recent vehicle registration data. These data were compiled from FHWA (2004), Federal Motor Carrier Safety Administra- tion (FMCSA), and Bureau of Transportation Statistics (BTS) sources for 2016 and 2017. The data for the breakdown of buses into categories for school buses, transit buses, and other buses (including motor coaches/intercity buses) is based on data from BTS and the National School Transportation Association [NSTA (2013)]. The data in Table 17 show that approximately 92% of registered vehicles in the United States are passenger vehicles, so passenger vehicles need to be represented among the Green Book design vehicles. Approximately 45% of the registered passenger cars are automobiles, while 55% are light trucks (pickup trucks, SUVs, and vans). The need for a light truck design vehicle is addressed in Section 5.2. Motorcycles represent approximately 3% of the vehicle fleet. However, the small size of a motorcycle, even if towing a trailer, makes it unlikely that a motorcycle would ever be appro- priate as a design vehicle. Heavy trucks constitute approximately 4.5% of registered vehicles in the United States. There are about three times as many registered single-unit trucks as there are registered tractors (which, except for a limited number of deadhead trips, serve as the power units for combination trucks). However, BTS data for 2016 (www.bts.gov/content/bus-profile) show that each combination truck travels five times as many vehicle miles per year as each single-unit truck (62,751 miles per vehicle per year for combination trucks versus 12,435 miles per vehicle per year for single-unit trucks). Overall, it is estimated that combination trucks travel 1.6 times as many vehicle miles per year on U.S. roads as single-unit trucks (181,000 million vehicle miles per year for combina- tion trucks versus 116,000 million vehicle miles per year for single-unit trucks). Buses constitute approximately 0.4% of the registered U.S. vehicle fleet. The best breakdown of bus types found to date indicates that school buses constitute approximately 49% of the bus fleet, transit buses constitute approximately 6% of the bus fleet, and other buses (including motor coaches/intercity buses) constitute approximately 45% of the bus fleet. FMCSA data for 2016 indicate that, on average, buses travel 16,750 miles per year, corresponding to 16,350 million vehicle miles per year in total bus travel. No reliable data have been found concerning total U.S. registrations for motor homes or trailers of various types. C H A P T E R 4 Assembly of Data on the Current Vehicle Fleet

32 Highway and Street Design Vehicles: An Update 4.2 Vehicle Specification Data Data on vehicle specifications, including dimensions, and, when available, turning radii of specific vehicle makes and models, were sought from internet searches of vehicle manufacturers’ websites and published vehicle characteristics data. Data were generally sought for the model year 2019 vehicles. The model year 2019 was the current model year when the research began, and 2019 vehicles were designed and manufactured before any supply chain disruptions that may have followed the COVID-19 pandemic. Vehicle types, for which reasonably complete specifications for a wide range of vehicle makes and models were found, included passenger vehicles (automobiles, minivans/vans, pickup trucks, and SUVs), single-unit trucks, intercity buses, school buses, transit buses, and motor homes. Vehicle dimensions that were sought, when available, included overall vehicle length, wheel- base (distance from frontmost axle to rearmost axle or center-of-rear-axle group), individual axle spacings, vehicle width, vehicle height, cab body length (for truck tractors), vehicle minimum turning radii, and vehicle body ground clearance. There were very few cases in which all these data were available for all makes and models for a given vehicle type. The most commonly avail- able data were overall vehicle lengths and wheelbases. The least commonly available data were turning radii and ground clearance. The vehicle specification data for individual vehicle makes and models were tabulated in spreadsheets, so they could be sorted to determine distributions of key dimensions by vehicle make and model. Where the variations in dimensions were substantial within a given vehicle make and model, separate records were made for each variation. However, in some cases, the various forms for a specific vehicle make and model represented only differences in user options or trim packages that did not affect the vehicle dimensions. In other cases, there were some minor variations (an inch or two) in dimensions among variations of a specific vehicle make and model; in these cases, the research team generally used the variation with the largest dimension. Vehicle type Number of registered vehicles Percentage of registered vehicles Passenger vehicles 248,840,000 91.9 Automobiles 111,180,000 41.0 Pickup trucks 47,860,000 17.7 Sport utility vehicles (SUVs) 73,580,000 27.2 Vans 16,220,000 6.0 Motorcycles 8,720,000 3.2 Heavy trucks 12,230,000 4.5 Single-unit trucks 9,340,000 3.4 Truck tractors for combination trucks 2,890,000 1.1 Busesa 980,000 0.4 School buses 480,000b 0.2 Transit buses 60,000c 0.02 Other buses (including intercity buses and motor coaches) 440,000 d 0.2 TOTAL 270,770,000 100.0 Sources: Adapted from FHWA (2004), FMCSA, Bureau of Transportation Statistics (2016, 2017), and other cited sources. a Total number of registered buses is based on BTS data (www.bts.gov/content/bus-profile). b Based on NSTA data for 2013 (https://s3-us-west-2.amazonaws.com/nsta/6571/Yellow-School-Bus-Industry-White-Paper.pdf). c Number of transit buses based on BTS data (www.bts.gov/content/transit-profile). d Computed from the preceding three values. Table 17. Summary of U.S. vehicle registration data.

Assembly of Data on the Current Vehicle Fleet 33 Each vehicle make and model, or variation of a make and model, was treated as an individual data point. Some vehicle makes and models have greater unit sales or are driven more miles than others. Ideally, the data on dimensions of vehicle makes and models would be weighted by units sold or vehicle miles of travel to provide a more complete view of the vehicles actually on the road. However, no data on vehicle units sold or vehicle miles of travel are generally available for individual vehicle makes and models. Therefore, of necessity, equal weight was assigned to each vehicle make and model (or make and model variation) in assessing distributions of vehicle dimensions. The distributions of key vehicle dimensions from vehicle specification data used in assessing the sizes for individual vehicle types are presented in Chapter 5. 4.3 Field Studies to Obtain Vehicle Dimension Data The vehicle specification data collection described in Section 4.2 provided information about most vehicle types of interest, except for combination trucks. The trailer lengths for combination trucks are generally limited by federal and state regulations, so no additional data were needed about trailer lengths. As explained in Chapter 5, the lengths of tractors that pull the trailers in combination trucks are not generally limited by state and federal regulation, so documentation of the tractor lengths and wheelbases was needed. However, no data were available to document how truck tractor lengths have changed over time. The vehicle specification data available for truck tractors are not directly useful in estimating the distributions of tractor lengths and wheelbases because nearly every tractor model sold to trucking companies can be custom ordered with a range of wheelbases. Therefore, truck operators order tractors with whatever dimensions best suit their intended operating environment. A method was needed to obtain data on truck tractor dimensions in actual use for specific truck types. To obtain current data on dimensions for truck tractors or other vehicle types, that could not be obtained through internet searches, the research team considered measuring truck tractors at weigh stations, truck stops, or terminal sites. Ultimately, this approach was not pursued because of the following: • Permission to use the weigh station, truck stop, or terminal site would need to be arranged with the facility operator. • If manual measurements were made, permission to measure a specific vehicle would need to be requested from the driver. Such permission might or might not be forthcoming. • Making manual measurements in the field would be time-consuming and labor-intensive. Because of these concerns, alternative approaches to obtaining vehicle measurements were investigated. A photographic approach to obtaining vehicle dimension data appeared to be most promising. A photographic approach was desirable because it would not necessarily be limited to weigh stations, truck stops, or terminal sites, and it could be conducted at any location with a suitable camera vantage point. The research team identified a technology to automate the measurement of vehicle dimensions from photographic images. Furthermore, obtaining photo- graphic images of all vehicles for a given period at a given site would help minimize any selection bias in deciding which vehicles to measure at that site. The approach to photographic data collection that was developed and tested involved placing a video camera on the roadside (preferably, but not necessarily, at an elevated location) and orienting the camera’s view perpendicular to the traffic stream. Figure 12 shows a typical camera setup with the camera pointing across the road. Figure 13 shows a typical vehicle photograph obtained from a camera oriented in this manner.

34 Highway and Street Design Vehicles: An Update Figure 12. Typical video camera setup for photographic data collection. Figure 13. Vehicle image from an actual video. The research team learned that its subcontractor, Texas A&M Transportation Institute (TTI), had developed a method for applying existing technology to make measurements of roadway features from video images. This same technology can be applied to make measurements of vehicle dimensions from video images. To obtain such measurements, the video camera was set up in a fixed orientation on the road- side at a specific site and not moved (and not refocused) for the entire study period at that site (typically 2 hours). Then, in the office, the video file was separated into individual video frames, and the video frames showing specific vehicle types of interest were selected and measured. A known dimension for scaling measurements was needed. The video images from each site could be calibrated since some trucks with van trailers that are 53 ft in length could be identified by noting a 53-ft marking on the side of the trailer (see example in the lower front corner of the trailer in Figure 13). (Note that when 53-ft trailers first came into widespread use, some states required a 53-ft marking on the side of the trailer. While this marking is no longer required, many 53-ft trailers still have such markings.) In addition, the lane widths at each site were measured from aerial photographs and used for calibration. Once the images for a specific site

Assembly of Data on the Current Vehicle Fleet 35 were calibrated by measuring several trailers known to be 53 ft in length and the known lane widths, any vehicle image from that video setup could be used to measure the vehicle dimensions. Preliminary testing with the 53-ft calibration vehicles established that the measured lengths of 53-ft trailers could be reproduced within ±0.4 ft or less than 1%. Figure 14 illustrates the use of measurement software to measure the dimensions of a specific vehicle. Once the video setup for a specific site has been calibrated, a research team member, using the measurement software, selected the image of a vehicle of interest, clicked on the points where each vehicle tire touches the roadway (which established the plane of the roadway lane), and then clicked on specific pairs of points on the video image of the vehicle to measure the distance between them. Figure 14 shows a sample vehicle for which trailer length (52.8 ft), tractor wheelbase (19 ft), and trailer wheelbase (39.1 ft) have been measured. Measurements made with the system are automatically captured in an Excel spreadsheet. Data using this approach were collected for 2-hour periods at sites in five states: Kansas, Missouri, Pennsylvania, Texas, and Washington. These states were selected to incorporate both geographical diversity and variations in vehicle size and weight regulations. The data collection sites are located on radial or circumferential interstate highways in urban or suburban portions of major metropolitan areas in each state. Data were obtained in this manner for approximately 2,260 vehicles of a variety of vehicle types, including 1,111 single-trailer combination trucks, 67 double-trailer combination trucks, and 5 triple-trailer combination trucks. Truck tractor dimensions, including length, wheelbase, and front overhang, were estimated from the photo images. Combination trucks incorporate a variety of trailer types, the most common being an enclosed van. The tractor dimensions for this research were based on the tractors being used to pull enclosed van trailers. The tractor dimensions derived from this data collection are presented in Section 5.4. The results for vehicle types other than combination trucks were checked for consistency with the results obtained from vehicle specification data. Figure 14. Measurement of selected dimensions for a typical truck.

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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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