National Academies Press: OpenBook

Guidelines for Traversability of Roadside Slopes (2019)

Chapter: Appendix C - CarSim Wrapper Program User Guide

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Suggested Citation:"Appendix C - CarSim Wrapper Program User Guide." National Academies of Sciences, Engineering, and Medicine. 2019. Guidelines for Traversability of Roadside Slopes. Washington, DC: The National Academies Press. doi: 10.17226/25539.
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Suggested Citation:"Appendix C - CarSim Wrapper Program User Guide." National Academies of Sciences, Engineering, and Medicine. 2019. Guidelines for Traversability of Roadside Slopes. Washington, DC: The National Academies Press. doi: 10.17226/25539.
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Suggested Citation:"Appendix C - CarSim Wrapper Program User Guide." National Academies of Sciences, Engineering, and Medicine. 2019. Guidelines for Traversability of Roadside Slopes. Washington, DC: The National Academies Press. doi: 10.17226/25539.
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Suggested Citation:"Appendix C - CarSim Wrapper Program User Guide." National Academies of Sciences, Engineering, and Medicine. 2019. Guidelines for Traversability of Roadside Slopes. Washington, DC: The National Academies Press. doi: 10.17226/25539.
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Suggested Citation:"Appendix C - CarSim Wrapper Program User Guide." National Academies of Sciences, Engineering, and Medicine. 2019. Guidelines for Traversability of Roadside Slopes. Washington, DC: The National Academies Press. doi: 10.17226/25539.
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Suggested Citation:"Appendix C - CarSim Wrapper Program User Guide." National Academies of Sciences, Engineering, and Medicine. 2019. Guidelines for Traversability of Roadside Slopes. Washington, DC: The National Academies Press. doi: 10.17226/25539.
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Suggested Citation:"Appendix C - CarSim Wrapper Program User Guide." National Academies of Sciences, Engineering, and Medicine. 2019. Guidelines for Traversability of Roadside Slopes. Washington, DC: The National Academies Press. doi: 10.17226/25539.
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Suggested Citation:"Appendix C - CarSim Wrapper Program User Guide." National Academies of Sciences, Engineering, and Medicine. 2019. Guidelines for Traversability of Roadside Slopes. Washington, DC: The National Academies Press. doi: 10.17226/25539.
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Suggested Citation:"Appendix C - CarSim Wrapper Program User Guide." National Academies of Sciences, Engineering, and Medicine. 2019. Guidelines for Traversability of Roadside Slopes. Washington, DC: The National Academies Press. doi: 10.17226/25539.
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Suggested Citation:"Appendix C - CarSim Wrapper Program User Guide." National Academies of Sciences, Engineering, and Medicine. 2019. Guidelines for Traversability of Roadside Slopes. Washington, DC: The National Academies Press. doi: 10.17226/25539.
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C-1 A P P E N D I X C CarSim Wrapper Program User Guide C.1 DRIVER INPUTS The following five driver inputs have been used: Driver Input Number Details 1 No input (tracking) 2 Panic steer, no brake (tracking) After 1.0 sec PRT delay on leaving the edge of travel lane, a 360-degree steer towards roadway is applied at the rate of 720 degree/s. 3 Panic steer and full ABS brake (tracking) After 1.0 sec PRT delay on leaving the edge of travel lane, a 360-degree steer towards roadway is applied at the rate of 720 degree/s. 4 Constant Steer, no brake (non-tracking) Vehicle encroaches with yaw rate of 15 degree/s (yawing towards roadway), with a constant steer angle of 360 degrees. 5 Constant steer and full ABS brake (non-tracking) Vehicle encroaches with yaw rate of 15 degree/s (yawing towards roadway), with a constant steer angle of 360 deg. ABS brakes fully applied.

C-2 Guidelines for Traversability of Roadside Slopes Coefficient of friction of 0.75 is used for the roadway and the shoulder surface. For all other surfaces, a coefficient of friction of 0.501 is used in the longitudinal direction and a maximum coefficient of 1.2 is used in the lateral direction, as determined by the friction ellipse model. C.3 SIMULATION STOPPING CONDITIONS A simulation is stopped if any of the following conditions is met: 1. Vehicle comes back on the shoulder after the initial encroachment. 2. Vehicle travels beyond a specified lateral offset (set at 100 ft from the roadside edge of the travel lane). 3. Vehicle’s speed reduces below a specified minimum (set at 5 mi/h). 4. Vehicle rolls more than a specified maximum roll (set at 65 degrees). The vehicle is considered to have overturned at this point. 5. Vehicle pitches more than a specified maximum pitch (set at 90 degrees). The vehicle is considered to have overturned at this point. 6. Vehicle has travelled for more than 10 s. C.4 SIMULATION FLAGGING CONDITIONS A simulation is flagged without stopping it when any of the following conditions is met: 1. Vehicle has rolled more than 55 degrees. 2. Vehicle has pitched more than 55 degrees. 3. Vehicle spins out (i.e., the forward velocity of the vehicle becomes zero while it still has lateral velocity). 4. Vehicle has a side slipped more than a specified value (currently set at 20 degrees). C.2 ROAD GEOMETRY The following table contains legend/labels used for different terrain parameters and their corresponding values from the simulation matrix: Legend Description Values RdS Roadway slope (1V:xH, x is the value listed) -50 ShldS Shoulder slope (1V:xH, x is the value listed) -25 Shld1W Shld2W Shoulder is entered in two segments that can have different friction coefficients 3 ft. 3 ft. Shld1Fric Shld2Fric Coefficient of friction for each shoulder segment 0.75 0.75 FS Foreslope (1V:xH, x is the value listed) -10, -6, -4, -3, and -2 FSW Foreslope width 8 and 16 ft BtW Ditch bottom width 0, 4, and 10 ft BS Backslope (1V:xH, x is the value listed) 6, 4, 3, and 2 BSW Backslope width 8 and 16 ft Spd Encroachment speed 45, 55, 65, and 75 mi/h EncAng Encroachment angle 10, 20, and 30 degrees DriverInput Driver input number (see driver input table) 1, 2, 3, 4, and 5

Carsim Wrapper Program User Guide C-3 Label Description Run No. Simulation case number. Unique for a single vehicle type only. Termination Describes if the simulation terminated normally, or if the simulation crashed. It has values of “Normal” or “ERROR”. Outcome Stopping condition that caused the run to stop. It has following values. - Time Exceeded - Returns - Stops - Gone Far - Overturns Description A brief description of the outcome High Roll Flag for high roll (> 55 degrees). It has value of 1 or 0 (1 = high roll) Max Roll Maximum vehicle roll during simulation (deg.) High Pitch Flag for high pitch (> 55 degrees). It has value of 1 or 0 (1 = high pitch) Max Pitch Maximum vehicle pitch during simulation (deg.) Sideslip Flag for side slipped vehicle (> 20 degrees). It has value of 1 or 0 (1 = vehicle sideslips) Max. Slip Maximum sideslip angle during simulation (degrees) Spinout Flag for vehicle spinout. It has value of 1 or 0 (1 = vehicle spins out) Max Lat. Vel (km/h) Maximum lateral vehicle velocity during simulation (km/h) Max Lat. Travel (m) Maximum distance vehicle travels laterally from edge of roadway (m) Xcg at sim. Stop (m) X-coordinates of vehicle’s sprung mass CG when simulation stops (m) Ycg at sim. Stop (m) Y-coordinates of vehicle’s sprung mass CG when simulation stops (m) Information about the terrain parameters is included in this file. The labels are the same as listed previously. C.6 INDIVIDUAL SIMULATION RESULTS A separate program that comes with Carsim is used to extract the desired results for individual simulations from a binary file containing all outputs generated by Carsim. The following outputs are currently being extracted (more can be extracted if needed). C.5 TABULATED OUTCOME OF SIMULATION ANALYSES To evaluate outcome of the simulations in bulk, an output file with file ending with “*Results_Out.csv” is created. This file contains a log of several important results from each simulation case, along with key information about the terrain. The information about the terrain is only available if the TTI’s wrapper program is used to generate the terrains. Key outcomes recorded in the *Results_Out.csv file are listed in the following table.

C-4 Guidelines for Traversability of Roadside Slopes Label Description Time Simulation time (seconds) XCG_SM X-coord. of vehicle’s sprung mass CG in global coords. (m) YCG_SM Y-coord. of vehicle’s sprung mass CG in global coords. (m) ZCG_SM Z-coord. of vehicle’s sprung mass CG in global coords. (m) VxBf_SM X-comp. velocity for vehicle’s sprung mass CG in body-fixed coord. sys. (km/h) VyBf_SM Y-comp. velocity for vehicle’s sprung mass CG in body-fixed coord. sys. (km/h) VzBf_SM Z-comp. velocity for vehicle’s sprung mass CG in body-fixed coord. sys. (km/h) AxBf_SM X-comp. accel. for vehicle’s sprung mass CG in body-fixed coord. sys. (g) AyBf_SM Y-comp. accel. for vehicle’s sprung mass CG in body-fixed coord. sys. (g) AzBf_SM Z-comp. accel. for vehicle’s sprung mass CG in body-fixed coord. sys. (g) Pitch Vehicle’s Euler pitch (degree) Roll_E Vehicle’s Euler roll (degree) Yaw Vehicle’s Euler yaw (degree) YawLocal Vehicle’s Euler yaw offset to zero at start of simulation (degree) Beta Side-slip angle of vehicle based on Vx and Vy (degree) Alpha_L1 Tire L1 lateral slip (L/R is Left/Right, 1/2 is front/rare axle) (degree) Alpha_L2 Tire L2 lateral slip (degree) Alpha_R1 Tire R1 lateral slip (degree) Alpha_R2 Tire R2 lateral slip (degree) Fx_L1 Tire L1 longitudinal force (N) Fx_L2 Tire L2 longitudinal force (N) Fx_R1 Tire R1 longitudinal force (N) Fx_R2 Tire R2 longitudinal force (N) Fy_L1 Tire L1 lateral force (N) Fy_L2 Tire L2 lateral force (N) Fy_R1 Tire R1 lateral force (N) Fy_R2 Tire R2 lateral force (N) Fz_L1 Tire L1 vertical force (N) Fz_L2 Tire L2 vertical force (N) Fz_R1 Tire R1 vertical force (N) Fz_R2 Tire R2 vertical force (N) Note: At time t = 0 s, all values shown in the individual simulation results should be ignored except the coordinates of the vehicle’s sprung mass CG, velocities of the sprung mass CG, and roll, pitch, and yaw angles. Remaining variables may have erroneous values at t = 0 s and should be ignored.

Carsim Wrapper Program User Guide C-5 C.7 MISCELLANEOUS INFORMATION Simulations are performed for each vehicle at a time. This is done as Carsim requires certain parts of the wrapper program to be hard-coded, which need to be modified for different vehicle types. Road files with horizontal curvatures and super elevation need to be generated manually. The wrapper program can perform additional simulations with these specialized terrains, but it cannot generate those terrains automatically.

Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America’s Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S. DOT United States Department of Transportation

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Geometric design practitioners in state transportation agencies have a new set of guidelines on probability of vehicle rollover based on various roadside design features. NCHRP Research Report 911: Guidelines for Traversability of Roadside Slopes will assist practitioners in the reduction of serious injury crashes associated with rollovers on roadside slopes.

Data from the National Automotive Sampling System (NASS) Crashworthiness Data System (CDS) shows that one-third of single-vehicle run-off-road (SVROR) crashes result in rollovers—the leading cause of fatalities in SVROR crashes. Three-quarters of these rollover crashes involve vehicles digging into the ground on embankments or in ditches after encroaching onto the roadside. Additionally, according to NASS data, pickup trucks, utility vehicles, and vans are overrepresented in rollover crashes due to higher centers of gravity. An increase in the percentage of light trucks in the vehicle fleet necessitates additional research and updates to the roadside safety guidelines.

The researchers conducted 43,000 simulations for various combinations of roadside slope configurations and geometric conditions that represent real-world crash scenarios.

The results helped to produce this guidance on the traversability of roadside slopes for a variety of roadside conditions—shoulder width, foreslope, and foreslope width. The guidelines are presented as probability of vehicle rollover that is defined as a function of various roadside design features.

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