Review of Truck Characteristics as Factors in Roadway Design (2003)

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C-1 APPENDIX C TURNING PERFORMANCE ANALYSIS OF SPECIFIC DESIGN VEHICLES One of the overall objectives of the research is to recom- mend appropriate changes to the design vehicles in the 2001 Green Book (1) and recommend vehicles for consideration as future design vehicles. This appendix presents an evaluation of the turning performance characteristics for several of the design vehicles included in the 2001 Green Book and addi- tional vehicles being considered for inclusion as design vehi- cles in future versions of the Green Book. This comparison was conducted using AutoTURN, a commercially available vehicle turn simulation software program. The evaluation was conducted in three phases. Phase I was defining the parameters of each vehicle to be investigated. Phase II consisted of modeling 180° turns with minimum turn- ing radii and determining the minimum distance between the center of the turning radius and the path of the rear axle set and the maximum distance between the center of the turning radius and the path of the front overhang. Phase III consisted of defining four 90° turns with turning radii of 15.2, 22.9, 30.5, and 45.7 m (50, 75, 100, and 150 ft), guiding each vehi- cle through each predefined turning path, and measuring the maximum offtracking, swept path width, and rear swingout. The remainder of this appendix presents each phase of the analysis. PHASE ONE—DEFINING VEHICLE PARAMETERS A total of 13 vehicles were modeled within AutoTURN, including 4 of the design vehicles defined in the 2001 Green Book and 9 vehicles considered for inclusion as design vehi- cles in future versions of the Green Book. The first step in evaluating the turning performance of each vehicle was to define the parameters of each vehicle. Within AutoTURN, the basic parameters to be defined include the longitudinal dimensions of the vehicle, the widths of the tractors and trail- ers, the tracks of the tractors and trailers, the minimum turn- ing radii, the maximum steering angles, and the maximum articulating angles. The user has several means to define the parameters of a vehicle in AutoTURN. The user can (1) create a customized vehicle by providing the input for all the vehicle parameters, (2) select a predefined design vehicle from within the soft- ware program in which case the vehicle parameters are pro- vided, or (3) select a predefined design vehicle from within the software program and modify the parameters as neces- sary. When selecting a predefined vehicle from within the program, the user can select design vehicles from sources such as the 2001 Green Book and the Canadian design guide. One of the limitations of AutoTURN concerns axle set- tings. The program does not account for the difference in turning performance between a single axle, double (tandem) axle, or tridem axle group. Because the type of axle has only a minor impact on the turning performance of a vehicle, this limitation of the program is not a concern. The program sim- ulates the turning performance of vehicles using calculations based upon the center of the axle groups for both the tractor and the trailer. Thus, when defining a vehicle, it is important to accurately specify the location of the center of the axle set or group. Selected Design Vehicles from the 2001 Green Book Four design vehicles in the 2001 Green Book were simu- lated within AutoTURN for comparison purposes. The sim- ulated vehicles included: • Single unit truck (SU) • WB-19 (WB-62) tractor-semitrailer • WB-20D (WB-67D) double trailer • WB-33B (WB-109D) double trailer The parameters of each design vehicle as defined in the 2001 Green Book are illustrated in Figures C-1 to C-4. Vehicles Considered for Inclusion as Future Design Vehicles Chapter 4 of this report presents the vehicles being consid- ered for inclusion as future design vehicles in the Green Book. This includes one single unit truck, four tractor-semitrailer combinations, and four double trailer combinations. This section presents figures that show the detailed parameters of each vehicle. More details are presented in the figures than are required for input into AutoTURN. When inputting the design parameters into AutoTURN, in most cases the design vehicle from the 2001 Green Book most similar to the proposed vehicle was selected from the AutoTURN program and then modified as appropriate. In doing so, default values for vehicle parameters such as max- imum steering angles and the maximum articulating angles were applied. For example, the WB-20 [WB-65 and WB-67] design vehicle in the 2001 Green Book is very similar to sev- eral of the proposed new design vehicles. Thus, the assumed steering angle for the WB-20 [WB-65 and WB-67] as speci- fied in the 2001 Green Book, or a value very similar to it, was

input as the steering angle for the respective proposed new design vehicles. The basis for selecting a value for an input parameter such as the maximum steering angle is significant because, in par- ticular, this parameter impacts the minimum turning radius of a vehicle. The minimum turning radius of a vehicle is a function of the maximum steering angle and the wheelbase of the tractor. The minimum turning radius of each vehicle was calculated as shown in Figure C-5. These calculations were verified with AutoTURN. In sev- eral cases, there were slight differences between the calcu- lated minimum turning radii and the minimum turning radii permitted within AutoTURN, in which case the minimum turning radii permitted within AutoTURN were recorded as the minimum turning radii for the vehicles. C-2 When defining the vehicle parameters for double-trailer combinations, there is a difference in the way the 2001 Green Book specifies articulation capabilities of double trailer com- binations and the way AutoTURN defines the articulation capabilities of double trailer combinations. The 2001 Green Book specifies an assumed steering angle, an assumed tractor/ trailer angle, and an assumed trailer/trailer angle. By con- trast, AutoTURN requires the input of two angles, the steer- ing angle and the articulating angle. When defining the param- eters of the proposed new double-trailer combinations, the design vehicles from the 2001 Green Book most similar to the proposed tractor double trailer combinations were selected as predefined design vehicles from within the software pro- gram, and the parameters were modified as appropriate. The default articulating angles were applied. For example, one Width: 8.00 ft Track: 8.00 ft Steering Angle: 31.70° Figure C-1. 2001 Green Book design vehicle: single unit (SU). Width: 8.50 ailer Track: 8.50 ft Tractor Width: 8.00 ft Tractor Track: 8.00 ft Trailer ft Tr Steering Angle: 28.40° Articulating Angle: 65.00° Figure C-2. 2001 Green Book design vehicle: WB-19 [WB-62] tractor semi-trailer.

of the proposed design vehicles is a double trailer combina- tion with two 16.15 m [53 ft] trailers. In the 2001 Green Book, the most similar vehicle to this double trailer combi- nation is the WB-33D [WB-109D], with two 14.63 m [48 ft] trailers. The WB-33D [WB-109D] was selected as prede- fined in the software program and modified to include 16.15 m [53 ft] trailers rather than 14.63 m [48 ft] trailers. The artic- ulating angle of the WB-33D [WB-109D], as predefined within AutoTURN, was used as the articulating angle for C-3 the proposed double trailer combination with 16.15 m [53 ft] trailers. Single-Unit Truck The new single-unit truck design vehicle recommended for inclusion in the Green Book is a three-axle truck with an overall length of 12.0 m [39.5 ft] (Figure C-6), designated as Tractor Width: 8.00 ft Tractor Track: 8.00 ft Trailer Width: 8.50 ft Trailer Track: 8.50 ft Steering Angle: 15.70 Tractor/Trailer Angle: 35.10 Trailer/Trailer Angle: 56.00 ° ° ° Figure C-3. 2001 Green Book design vehicle: WB-20D [WB-67D] double trailer. Tractor Width: 8.00 ft Tractor Track: 8.00 ft Trailer Width: 8.50 ft Trailer Track: 8.50 ft Steering Angle: 12.70 Tractor/Trailer Angle: 45.00 Trailer/Trailer Angle: 70.00 ° ° ° Figure C-4. 2001 Green Book design vehicle: WB-33B [WB-109D] double trailer.

C-4 Centerline of Steering Axle Centerline of Drive Axle Maximum Steering Angle Maximum Steering Angle Turning Radius Ef fe ct iv e W he el ba se o f T ra ct o r Centerline Turning Radius = Effective Wheelbase Sin (Max. Steering Angle) Ef fe ct iv e W he el ba se o f T ra ct o r Ef fe ct iv e W he el ba se o f T ra ct o r Figure C-5. Minimum centerline turning radius calculations. Width: 8.00 ft Track: 8.00 ft Steering Angle: 31.80° Figure C-6. Single unit truck. the SU-8 [SU-25] design vehicle. The minimum centerline turning radius of this single unit truck is 14.5 m [47.5 ft]. In comparison, the single-unit design vehicle in the 2001 Green Book is a two-axle truck with an overall length of 9.15 m [30 ft]. The primary differences between the two vehicles are the number of axles, the overall length of the vehicles, and the wheelbases. WB-20 [WB-67] Tractor-Semitrailer The WB-20 [WB-67] tractor-semitrailer design vehicle is a variation of the WB-20 [WB-65] design vehicle already illustrated in the 2001 Green Book. This configuration has a 16.2 m [53 ft] trailer; the rear axles are located at the extreme rear of the trailer, with a KCRT of 13.9 m [45.5 ft] (see Fig- ure C-7). The minimum centerline turning radius of this WB-20 [WB-67] tractor-semitrailer configuration is 12.50 m [41.0 ft]. The only difference between the WB-20 [WB-67] design vehicle and the WB-20 [WB-65] design vehicle shown in the Green Book is the KCRT distance, which is 13.9 m [45.5 ft], rather than 13.3 m [43.5 ft]. WB-20 [WB-67] Tractor-Semitrailer: 12.5 m [41 ft] KCRT Another vehicle investigated is a variation of the WB-20 [WB-67] design vehicle discussed above. This variation, shown in Figure C-8, has the rear trailer axles pulled for-

Tractor Width: 8.00 ft Tractor Track: 8.00 ft Trailer Width: 8.50 ft Trailer Track: 8.50 ft Steering Angle: 28.40 Articulating Angle: 75.00 ° ° Figure C-7. WB-20 [WB-67] tractor-semitrailer. 1.22 m [4.0 ft] [3.0 ft] 0.91 m [4.42 ft] [4.2 ft] 1.28 m 5.30 m [17.4 ft] 5.95 m [19.5 ft] 4.57 m [15.0 ft] [4.0 ft] 1.22 m 2.74 m [9 ft] 19.05 m [62.5 ft] Wheelbase 1.35 m 22.40 m [73.5 ft] 12.50 m [41 ft] 16.15 m [53.0 ft] Trailer Tractor Width: 8.00 ft Tractor Track: 8.00 ft Trailer Width: 8.50 ft Trailer Track: 8.50 ft Steering Angle: 28.40 Articulating Angle: 75.00 ° ° Figure C-8. WB-20 [WB-67] tractor-semitrailer—12.5 m [41 ft] KCRT distance. C-5 ward to a KCRT distance of 12.5 m [41 ft], which is the maximum permitted KCRT distance permitted in many states. Pulling the rear axles forward creates a rear overhang of 2.7 m [9 ft]. WB-22 [WB-71] Tractor-Semitrailer Another vehicle considered for possible future inclusion in the Green Book is the WB-22 [WB-71] design vehicle. This vehicle is a tractor-semitrailer configuration with a 17.34 m [57 ft] trailer (see Figure C-9). The rear axles are located at the extreme rear of the trailer, with a KCRT distance of 15.1 m [49.5 ft]. The minimum centerline turning radius of this WB- 22 [WB-71] tractor-semitrailer configuration is 12.7 m [41.5 ft]. WB-22 [WB-71]: Tractor-Semitrailer— 12.5 m [41 ft] KCRT Distance A variation of the WB-22 [WB-71] design vehicle was also investigated. This variation, shown in Figure C-10, has the rear axles pulled forward to a KCRT distance of 12.5 m [41 ft], which is the maximum permitted KCRT distance in many states. Pulling the rear axles forward creates a rear overhang of 4.0 m [13 ft].

C-6 Tractor Width: 8.00 ft Tractor Track: 8.00 ft Trailer Width: 8.50 ft Trailer Track: 8.50 ft Steering Angle: 28.40 Articulating Angle: 75.00 ° ° Figure C-9. WB-22 [WB-71] tractor-semitrailer. 1.22 m [4.0 ft] [3.0 ft] 0.91 m [4.2 ft] 1.28 m 5.30m [17.4 ft] 5.95 m [19.5 ft] 4.57 m [15.0 ft] [13 ft] 3.96 m [4.0 ft] 1.22 m 19.05 m [62.5 ft] Wheelbase [4.42 ft] 1.35 m 23.62 m [77.5 ft] 17.37 m [57.0 ft] Trailer 12.50 m [41 ft] Tractor Width: 8.00 ft Tractor Track: 8.00 ft Trailer Width: 8.50 ft Trailer Track: 8.50 ft Steering Angle: 28.40 Articulating Angle: 75.00 ° ° Figure C-10. WB-22 [WB-71]: Tractor-semitrailer: 12.5 m [41 ft] KCRT distance. WB-23D [WB-77D]: Double-Trailer Combination with Twin 10.1-m [33-ft] Trailers This double-trailer combination for possible future inclusion in the Green Book has an overall length of 24.8 m [81.5 ft] with two 10.1-m [33-ft] trailers (see Figure C-11). It has tandem axles at both the front and rear of each trailer. The KCRT dis- tance is 8.0 m [26.5 ft]. It has a minimum centerline turning radius of 13.7 m [45.0 ft]. WB-37D [WB-120D]: Turnpike Double Combination with Two 16.2 m [53 ft] Trailers This Turnpike Double combination for possible future inclusion in the Green Book has an overall length of 39.3 m [129.3 ft] with two 16.2 m [53 ft] trailers (see Figure C-12). It has tandem axles at both the front and rear of each trailer. The KCRT distance is 12.5 m [41 ft]. It has a minimum center- line turning radius of 23.8 m [78.0 ft]. WB-28D (WB-92D): Rocky Mountain Double Trailer Combination This double-trailer combination recommended for inclusion in the Green Book has an overall length of 30.0 m [98.3 ft] (see Figure C-13). The first trailer has a length of 14.6 m [48.0 ft], while the second trailer has a length of 8.7 m [28.5 ft]. The first trailer has tandem axles at both the front and rear of the trailer, while the second trailer has single axles at both the front and

C-7 Tractor Width: 8.00 ft Tractor Track: 8.00 ft Trailer Width: 8.50 ft Trailer Track: 8.50 ft Steering Angle: 15.60 Articulating Angle: 70.00 ° ° Figure C-11. WB-23D [WB-77D] double trailer combination. Tractor Width: 8.00 ft Tractor Track: 8.00 ft Trailer Width: 8.50 ft Trailer Track: 8.50 ft Steering Angle: 12.60 Articulating Angle: 70.00 ° ° Figure C-12. WB-37D [WB-120D] double trailer combination. Tractor Width: 8.00 ft Tractor Track: 8.00 ft Trailer Width: 8.50 ft Trailer Track: 8.50 ft Steering Angle: 12.60 Articulating Angle: 70.00 ° ° Figure C-13. WB-28D [WB-92D] double trailer combination.

rear of the trailer. It has a minimum centerline turning radius of 23.8 m [78.0 ft]. WB-23BD [WB-75BD]: B-Train Double-Trailer Combination This B-train double trailer combination for potential future inclusion in the Green Book has an overall length of 24.2 m [79.5 ft] (see Figure C-14). A B-train combination has a first trailer with a fifth wheel mounted on a dolly at the rear. The second trailer is a semitrailer that rests on the fifth wheel attached to the first trailer. The length of the first trailer is 8.5 m [28.0 ft], and the length of the second trailer is 9.6 m [31.5 ft]. It has a minimum turning radius of 12.07 m [39.6 ft]. The dimensions of this proposed truck are similar to those found in the Geometric Design Guide for Canadian Roads (16). SUMMARY OF INPUT PARAMETERS FOR VEHICLES CONSIDERED Table C-1 presents a summary of the input parameters of each vehicle modeled within AutoTURN. The top portion of the table provides the input parameters for selected design vehicles from the 2001 Green Book, while the bottom por- tion of the table provides the input parameters for the pro- posed new design vehicles. PHASE II—MODELING OF MINIMUM 180-DEGREE TURNS In Phase II, 180-degree turns with minimum turning radii were modeled for seven vehicles being considered for possible inclusion in the Green Book. These vehicles included the seven SU-8 [SU-25], WB-20 [WB-67], WB-22 [WB-71], WB-23D [WB-77D], WB-37D [WB-120D], WB-28D [WB-92D], and WB-23BD [WB-75BD] design vehicles. The capabilities of these seven vehicles to negotiate 180-degree turns at minimum turning radii are presented in Figures C-15 to C-21. The figures show the centerline turning radius of the front axle, the mini- mum turning radius of the driver’s side front tire, the minimum distance between center of the turning radius and the path of the rear axle set, and the maximum distance between the cen- ter of the turning radius and the path of the front overhang. Fig- ures C-15 to C-21 can be used in future versions of the Green Book if a decision is made to add these design vehicles. Minimum 180-degree turns were not modeled for two of the proposed new design vehicles presented earlier in this appendix, the WB-20 [WB-67] and WB-22 [WB-71] with KCRT distances of 12.5 m [41 ft]. These trucks have nearly identical turning performance to the very similar turning capabilities of the WB-19 [WB-62] design vehicle, so no separate turning plots are needed. The revised WB-19 [WB- 62] design vehicle proposed for future use in the Green Book also has a KCRT distance of 12.5 m [41 ft]. Table C-2 summarizes the critical turning parameters shown in Figures C-15 to C-21. For comparative purposes, Table C-2 also summarizes these same critical turning para- meters for the single unit truck (SU), WB-19 (WB-62) tractor- semitrailer, WB-20D (WB-67D) double trailer, and WB-33B (WB-109D) double trailer design vehicles from the 2001 Green Book. The results are presented by vehicle classifica- tion: single unit, tractor-semitrailer, and double trailer com- bination. When comparing the turning characteristics of the respective vehicles in the different vehicle classes, several points are worth noting: C-8 Tractor Width: 8.00 ft Tractor Track: 8.00 ft Trailer Width: 8.50 ft Trailer Track: 8.50 ft Steering Angle: 29.50 Articulating Angle: 70.00 ° ° Figure C-14. WB-23BD [WB-75BD] double trailer combination.

C-9 Design Vehicles Width and Track of Tractor (A) Width and Track of Trailer (B) Overall Length (C) Overall Wheelbase (D) Cab Length (E) Front Overhang (F) Steer Axle to 2nd Axle Set (G) King Pin to Rear Axle Set (H) 2nd Axle Set to 3rd Axle Set (I) 3rd Axle Set to 4th Axle Set (J) 4th Axle Set To 5th Axle Set (K) Rear Overhang of 1st Trailer (L) Rear Overhang of 2nd Trailer (M) Overall Length of 1st Trailer (N) Overall Length of 2nd Trailer (O) Min. Centerline Turning Radius of Front Axle (P) Max. Steering Angle (Degrees) (Q) Max. Articulating Angle (Degrees) (R) AASHTO 2001 Green Book Design Vehicles SU 8 30 20 4 20 6 38.0 31.7 WB-62 8 8.5 68.5 62 15 4 19.5 40.5 40.5 4.5 48 41.0 28.4 65 WB- 67D 8 8.5 72.33 67 6.5 2.33 11 23 23 10 23 3 3 28.5 28.5 41.0 15.7 70 WB- 109D 8 8.5 114.03 109.2 6.5 2.33 12.2 40.5 40.0 14.5 40.5 4.5 4.5 48 48 56.0 12.7 70 Possible New Design Vehicles SU-25 8 39.5 25 4 25 10.5 47.5 31.8 WB-67 8 8.5 73.5 67 15 4 19.5 45.5 45.5 4.5 53 41.0 28.4 75 WB-67 (41 ft KCRT) 8 8.5 73.5 62.5 15 4 19.5 41 41 9 53 41.0 28.4 75 WB-71 8 8.5 77.5 71 15 4 19.5 49.5 49.5 4.5 57 41.5 28.4 75 WB-71 (41 ft KCRT) 8 8.5 77.5 62.5 15 4 19.5 41 41 13 57 41.0 28.4 75 WB- 77D 8 8.5 81.50 77.2 6.5 2.33 12.2 26.5 25.5 11 26.5 4 4 33 33 45.0 15.6 70 WB- 120D 8 8.5 129.33 120.0 9.5 2.33 17.5 41 40.5 19 41 9 9 53 53 78.0 12.6 70 WB- 92D 8 8.5 98.25 92.0 9.5 2.33 17.5 41 40.5 11 23 4 3 48 28.5 78.0 12.6 70 WB- 75BD 8 8.5 79.53 74.53 9.5 2.33 17.5 29.5 29.5 31 27.7 4.5 28 31.5 39.6 29.5 70 A – Width and track of tractor or vehicle body if SU. B – Width and tract of trailer body. C – Overall length of vehicle, measured from front bumper to rear bumper. D – Overall length of wheelbase, measured from center of steering axle to center of rear axle. E – Length of cab, measured from front bumper to rear of cab. F – Front overhang, measured from front bumper to center of steering axle. G – Distance between center of steer axle to center of second axle group. H – Distance from kingpin to center of rear axle group I – Distance between center of second axle group to center of third axle group. J – Distance between center of third axle group to center of fourth axle group. K – Distance between center of fourth axle group to center of fifth axle group. L – Rear overhang on first trailer or first vehicle, measured from center of rear axle group to rear bumper. M – Rear overhang on second trailer, measured from center of rear axle group to rear bumper. N – Overall length of first trailer. O – Overall length of second trailer. P – Minimum centerline turning radius of front axle. Q – Maximum steering angle. R – Maximum articulating angle. NOTE: All lengths and widths are in feet. TABLE C-1 Input parameters of vehicles considered in turning performance evaluation

Single Unit Vehicles • The minimum turning radius of the proposed single unit design vehicle is 2.9 m [9.5 ft] greater than the mini- mum turning radius of the single unit design vehicle in the 2001 Green Book. • The difference between the minimum turning radius and the maximum distance to the path of the front overhang is equivalent for both vehicles. C-10 • The minimum distance between the path of the rear axle set and the center of the turn is greater for the proposed single unit design vehicle than the single unit design vehicle in the 2001 Green Book. • The difference between minimum turning radius and the minimum distance between the path of the rear axle set and the center of the turn is greater for the proposed single unit design vehicle than for the single unit design vehicle in the 2001 Green Book which indicates that the Figure C-15. Minimum 180º turn: single unit truck.

proposed single unit design vehicle has greater offtrack- ing and a wider swept path width than the single unit design vehicle in the 2001 Green Book. Tractor-Semitrailers • The minimum turning radius of the proposed WB-22 [WB-71] design vehicle is 0.15 m [0.5 ft] greater than C-11 the turning radii of the other tractor-semitrailer design vehicles, but for practical purposes the minimum turn- ing radii of all the proposed tractor-semitrailer design vehicles and the WB-19 [WB-62] design vehicle in the 2001 Green Book are equivalent. Direct calculations of the minimum turning radii for all tractor-semitrailers (as per Figure C-5) indicates a minimum turning radii of 13.7 m [45 ft] for all tractor-semitrailers. Figure C-16. Minimum 180º turn: WB-20 [WB-67] tractor-semitrailer.

Although the minimum turning radii for all the tractor- semitrailers are approximately equivalent, the longer wheel- bases of the WB-20 [WB-67] and the WB-22 [WB-71] proposed design vehicles result in considerably smaller min- imum distances between the path of the rear axle set and the center of the turn for these two vehicles compared to the other tractor-semitrailer combinations. In fact, the rear axle set of the WB-22 [WB-71] tracks on the inside of the turning center. C-12 Double Trailer Combinations • The proposed WB-37D [WB-120D] and WB-28D [WB- 92D] design vehicles have significantly greater mini- mum turning radii compared to the other double trailer combinations. • There is a wide range in the minimum distances between the path of the rear axle set and the center of the turn for Figure C-17. Minimum 180º turn: WB-22 [WB-71] tractor-semitrailer.

C-13 Figure C-18. Minimum 180º turn: WB-23D [WB-77D] double trailer combination. the double trailer combinations, with a minimum of 2.36 m [7.7 ft] and a maximum of 16.9 m [55.4 ft]. PHASE III—MODELING OF 90-DEGREE TURNS Phase III consisted of modeling 90-degree right turns with centerline turning radii of 15.2, 22.9, 30.5, and 45.7 m (50, 75, 100, and 150 ft) and comparing the capabilities of the pro- posed design vehicles as they negotiated through the respec- tive turns to the capabilities of similar design vehicles in the 2001 Green Book. The parameters of specific interest in this sensitivity analysis included maximum offtracking, swept path width, and rear swingout. These parameters were measured directly from turning path plots generated by AutoTURN. The procedures for measuring the three parameters from the plots are described, and the results are then presented by vehicle classification: single unit, tractor-semitrailer, and double trailer combination.

Estimating Maximum Offtracking Offtracking is defined as the radial offset between the path of the centerline of the front axle of the tractor and the path of the centerline of the rearmost trailer axle set. There are two types of offtracking, referred to as low-speed and high-speed offtracking. This analysis focuses on low-speed offtracking which occurs as vehicles traverse horizontal curves at low speed. C-14 To estimate the maximum offtracking as a vehicle negoti- ates a 90-degree right turn, the path of the center of the front tractor axle (steering axle) is specified and the path of the inside rear axle set of the trailer generated by AutoTURN. Fig- ure C-22 provides an example of one of the turning path plots. The example shows the proposed WB-23D [WB-77D] double trailer combination negotiating a 90-degree turn with a 15.2 m [50 ft] turning radius. The figure also shows the paths of other vehicle parts. The offtracking was quantified Figure C-19. Minimum 180º turn: WB-37D [WB-120D] double trailer combination.

by bringing the AutoTURN plot into AutoCAD and scaling the appropriate distances. The largest radial distance between the two paths (that of the center of the front axle and that of the inside rear axle set) was scaled. Measurements were taken along the entire length of the curve until a maximum radial distance was determined. In Figure C-22, several of the actual measurements are displayed with the maximum dis- tance shown with a box around it. Since offtracking is mea- sured to the centerline of both the front and rear axle set, half the width of the rear axle set was subtracted from the measured C-15 radial distance to provide an estimate of the maximum off- tracking. For example, the tractor-semitrailers and the double trailer combinations had 2.6 m [8.5 ft] wide trailers. There- fore, 1.3 m [4.25 ft] was subtracted from the measured radial distance to determine the maximum offtracking of these vehicle types, while 1.2 m [4.0 ft] was subtracted for the sin- gle unit trucks. Thus, for the given example of the proposed WB-23D [WB-77D] design vehicle negotiating a 90-degree turn with a 15.2 m [50 ft] radius, the maximum offtracking is 4.3 m [14.2 ft]. Figure C-20. Minimum 180º turn: WB-28D [WB-92D] double trailer combination.

Estimating Maximum Swept Path Width Swept path width is defined as the radial distance between the two paths of the outside front tractor tire and the inside rear axle set of the trailer. Conceptually, the maximum swept path width of a vehicle negotiating a turn occurs at the same location as the maximum offtracking. Thus, to estimate the maximum swept path width, half the width of the front trac- tor axle and half the width of the rearmost trailer axle were added to the maximum offtracking estimate. Continuing with the given example of the proposed WB-23D [WB-77D] C-16 design vehicle negotiating a 90-degree turn with a 15.2 m [50 ft] radius, the maximum offtracking is 4.3 m [14.2 ft]. Half the width of the front tractor axle is 1.2 m [4.0 ft], and half the width of the rear trailer axle is 1.3 m [4.25 ft]. Thus, the max- imum swept path width for the proposed WB-23D [WB-77D] design vehicle under the given scenario is 6.8 m [22.4 ft]. Estimating Maximum Rear Swingout The rear of a trailer generally overhangs the rear axle set. During a turn the rear of the trailer swings to the outside of Figure C-21. Minimum 180º turn: WB-23BD [WB-75BD] double trailer combination.

C-17 the path of the rear axle set. This rear swingout is a func- tion of the trailer wheelbases, the radius of the turn, and other dimensions of the vehicle. The procedures for esti- mating the maximum rear swingout were slightly different than for estimating the maximum offtracking and swept path width. Conceptually, maximum rear swingout is the maximum radial distance between the path of the outside rear axle set and the path of the outside rear corner of the trailer. AutoTURN is able to trace the path of the rear axle set of the trailer as it negotiates a turn but is unable to trace the path of the outside rear portion of the trailer. Therefore, it is not feasible to measure the radial distance between the continuous paths of the respective portions of a vehicle. However, AutoTURN has a function that draws vehicles at different intervals along the curve. Using this function, vehicles were drawn at very small intervals (i.e., 10 percent of the vehicle length) through the entire curve. These draw- ings showed the location of the outside rear corner of the trailer with respect to the path of the rear axle set and enabled measurement of the rear swingout. This proce- dure introduces some error in the measurement of the rear swingout because distances are not measured between continuous paths of the respective portions of the vehicle, but drawing the vehicles at very small intervals minimized this error. Figure C-23 illustrates measurement of the rear swingout for the WB-19 [WB-62] design vehicle while negotiating a 90-degree turn with a 15.2-m [50-ft] radius. The upper left portion of the figure shows vehicles drawn at various intervals along the same curve. The bottom right por- tion of the figure is a close-up of the rear portion of the vehi- cle at a particular location/instant along the curve and shows the radial distance between the path of the outside rear axle set and the location of the outside rear of the trailer. Summary of Results This section presents a summary of the turning perfor- mance results. The results are presented by vehicle classifi- cation. Table C-3 provides a comparison of turning capabil- ities of the proposed single unit design vehicle to the single unit design vehicle in the 2001 Green Book. Table C-4 pro- vides a comparison of the turning capabilities of the pro- posed tractor-semitrailer combinations to that of the WB-19 [WB-62] design vehicle. Table C-5 provides a comparison of the turning capabilities of the proposed double trailer combi- nations to those of the WB-20D [WB-67D] and WB-33D [WB-109D] design vehicles in the 2001 Green Book. When comparing the turning characteristics of the respec- tive vehicles while negotiating 90-degree turns with various turning radii, several points are worth noting: TABLE C-2 Summary of minimum 180-degree turning capabilities Design vehicles Minimum turning radius (ft) Maximum distance to path of front overhang (ft) Minimum distance between path of rear axle set and center of turn (ft) Single Unit Vehicles SU-25 51.5 53.0 36.4 SU 42.0 43.5 28.3 Tractor-Semitrailers WB-67 45.0 46.4 1.8 WB-67* (41 ft KCRT) 45.0 46.4 7.9 WB-71 45.5 46.9 2.5** WB-71* (41 ft KCRT) 45.0 46.4 7.9 WB-62 45.0 46.4 7.9 Double Trailer Combinations WB-77D 49.0 49.5 19.8 WB-120D 82.0 82.4 46.3 WB-92D 82.0 82.4 55.4 WB-75BD 43.6 44.2 7.7 WB-67D 45.0 45.5 19.3 WB-109D 60.0 60.4 14.9 * Measurements same as for WB-62 in 2001 Green Book ** Measured to the inside of the center of the turning radius

C-18 Figure C-22. Sample offtracking estimates.

Figure C-23. Sample rear swingout estimates. TABLE C-3 Turning capabilities of selected single-unit trucks Design vehicle Proposed design vehicle 2001 Green Book Turning capabilities Single Unit (SU) Wheelbase = 25 ft Single Unit (SU) Wheelbase = 20 ft Minimum turning radius 47.5 ft 38.0 ft 50 ft turning radiusa 6.13 ft 3.80 ft 75 ft turning radius 4.26 ft 2.74 ft 100 ft turning radius 3.21 ft 1.81 ft Maximum Offtracking 150 ft turning radius 2.13 ft 1.12 ft 50 ft turning radius 14.13 ft 11.80 ft 75 ft turning radius 12.26 ft 10.74 ft 100 ft turning radius 11.21 ft 9.81 ft Maximum Swept Path Width 150 ft turning radius 10.13 ft 9.12 ft 50 ft turning radius 1.07 ft 0.35 ft 75 ft turning radius 0.73 ft 0.24 ft 100 ft turning radius 0.53 ft 0.18 ft Maximum Rear Swingout 150 ft turning radius 0.35 ft 0.12 ft a Centerline turning radius.

C-20 TABLE C-4 Turning capabilities of selected tractor-semitrailer combinations Design vehicle Proposed design vehicle 2001 Green Book Turning capabilities WB-67 WB-67 (41 ft KCRT) WB-71 WB-71 (41 ft KCRT) WB-62 Minimum turning radius 41.0 ft 41.0 ft 41.5 ft 41.0 ft 41.0 ft 50 ft turning radiusa 19.38 ft 17.02 ft 21.51 ft 17.02 ft 16.76 ft 75 ft turning radius 15.10 ft 13.06 ft 17.01 ft 13.06 ft 12.83 ft 100 ft turning radius 12.08 ft 10.32 ft 13.75 ft 10.32 ft 10.12 ft Maximum Offtracking 150 ft turning radius 8.34 ft 7.04 ft 9.60 ft 7.04 ft 6.90 ft 50 ft turning radius 27.63 ft 25.27 ft 29.76 ft 25.27 ft 25.01 ft 75 ft turning radius 23.35 ft 21.31 ft 25.26 ft 21.31 ft 21.08 ft 100 ft turning radius 20.33 ft 18.57 ft 22.00 ft 18.57 ft 18.37 ft Maximum Swept Path Width 150 ft turning radius 16.59 ft 15.29 ft 17.85 ft 15.29 ft 15.15 ft 50 ft turning radius 0.17 ft 0.69 ft 0.17 ft 1.45 ft 0.18 ft 75 ft turning radius 0.14 ft 0.51 ft 0.13 ft 1.08 ft 0.14 ft 100 ft turning radius 0.10 ft 0.41 ft 0.10 ft 0.84 ft 0.09 ft Maximum Rear Swingout 150 ft turning radius 0.07 ft 0.27 ft 0.07 ft 0.61 ft 0.06 ft a Centerline turning radius. Design vehicle Proposed design Vehicle 2001 Green Book Turning capabilities WB- 77D WB- 120D WB- 92D WB- 77BD WB- 67D WB- 109D Minimum turning radius 49.0 82.0 ft 82.0 ft 43.5 ft 45.0 ft 60.0 ft 50 ft turning radiusa 14.18 ft *** *** 15.63 ft 11.47 ft *** 75 ft turning radius 10.56 ft *** *** 11.70 ft 8.31 ft *** 100 ft turning radius 8.16 ft 17.87 ft 12.71 ft 9.10 ft 6.31 ft 17.05 ft Maximum Offtracking 150 ft turning radius 5.45 ft 12.59 ft 8.73 ft 6.10 ft 4.20 ft 11.97 ft 50 ft turning radius 22.43 ft *** *** 23.88 ft 19.72 ft *** 75 ft turning radius 18.81 ft *** *** 19.95 ft 16.56 ft *** 100 ft turning radius 16.41 ft 26.12 ft 20.96 ft 17.35 ft 14.56 ft 25.30 ft Maximum Swept Path Width 150 ft turning radius 13.70 ft 20. 84 ft 16.98 ft 14.35 ft 12.45 ft 19.22 ft 50 ft turning radius 0.13 ft *** *** 0.17 ft 0.08 ft *** 75 ft turning radius 0.11 ft *** *** 0.12 ft 0.05 ft *** 100 ft turning radius 0.08 ft 0.37 ft 0.05 ft 0.10 ft 0.05 ft 0.09 ft Maximum Rear Swingout 150 ft turning radius 0.06 ft 0.27 ft 0.04 ft 0.07 ft 0.03 ft 0.06 ft *** Vehicle unable to negotiate a turn with the respective turning radius. a Centerline turning radius. TABLE C-5 Turning capabilities of select double-trailer combinations • The greatest differences in the turning characteristics between the respective vehicles occur along turns with smaller turning radii. • It appears that rear swingout is not as much of a concern as previously thought by many designers and researchers, for two reasons: 1. Maximum rear swingout values are relatively small, and 2. Maximum rear swingout occurs within the bound- aries of the swept path width of the vehicle as it negotiates the turn (see Figure C-23), which implies that the path of the front outside of the tractor is more critical to intersection and horizontal curve design than the path of the rear outside corner of the trailer.