National Academies Press: OpenBook

Guidelines for Cost-Effective Safety Treatments of Roadside Ditches (2021)

Chapter: APPENDIX B. CARSIM WRAPPER PROGRAM USERS GUIDE

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Suggested Citation:"APPENDIX B. CARSIM WRAPPER PROGRAM USERS GUIDE." National Academies of Sciences, Engineering, and Medicine. 2021. Guidelines for Cost-Effective Safety Treatments of Roadside Ditches. Washington, DC: The National Academies Press. doi: 10.17226/26127.
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Suggested Citation:"APPENDIX B. CARSIM WRAPPER PROGRAM USERS GUIDE." National Academies of Sciences, Engineering, and Medicine. 2021. Guidelines for Cost-Effective Safety Treatments of Roadside Ditches. Washington, DC: The National Academies Press. doi: 10.17226/26127.
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Suggested Citation:"APPENDIX B. CARSIM WRAPPER PROGRAM USERS GUIDE." National Academies of Sciences, Engineering, and Medicine. 2021. Guidelines for Cost-Effective Safety Treatments of Roadside Ditches. Washington, DC: The National Academies Press. doi: 10.17226/26127.
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Suggested Citation:"APPENDIX B. CARSIM WRAPPER PROGRAM USERS GUIDE." National Academies of Sciences, Engineering, and Medicine. 2021. Guidelines for Cost-Effective Safety Treatments of Roadside Ditches. Washington, DC: The National Academies Press. doi: 10.17226/26127.
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Page 263
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Suggested Citation:"APPENDIX B. CARSIM WRAPPER PROGRAM USERS GUIDE." National Academies of Sciences, Engineering, and Medicine. 2021. Guidelines for Cost-Effective Safety Treatments of Roadside Ditches. Washington, DC: The National Academies Press. doi: 10.17226/26127.
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Page 264

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B-1 APPENDIX B. CARSIM WRAPPER PROGRAM USERS’ GUIDE

B-2 CarSim Wrapper Program Users’ Guide Simulation Analysis Details and Glossary 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-deg steer towards roadway is applied at the rate of 720 deg/s. 3 Panic steer and full ABS brake (tracking) After 1.0 sec PRT delay on leaving the edge of travel lane, a 360-deg steer towards roadway is applied at the rate of 720 deg/s. 4 Constant Steer, no brake (non-tracking) Vehicle encroaches with yaw rate of 15 deg/s (yawing towards roadway), with a constant steer angle of 360 deg. 5 Constant steer and full ABS brake (non-tracking) Vehicle encroaches with yaw rate of 15 deg/s (yawing towards roadway), with a constant steer angle of 360 deg. And ABS brakes fully applied. 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 deg. DriverInput Driver input number (see driver input table) 1, 2, 3, 4, and 5 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.

B-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 traveled for more than 10 seconds. 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). 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 outcome recorded in the *Results_Out.csv file are listed in the following table. 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 deg.). 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 deg.). 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 deg.). It has value of 1 or 0 (1 = vehicle sideslips) Max. Slip Maximum sideslip angle during simulation (deg.)

B-4 Spinout Flag for vehicle spinout. It has value of 1 or 0 (1 = vehicle spins out) Max Lat. Vel (km/h) Max. lateral vehicle velocity during simulation (km/h) Max Lat. Travel (m) Max. distance vehicle travels laterally from edge of roadway (m) Xcg at sim. Stop (m) X-coord. of vehicle’s sprung mass CG when simulation stops (m) Ycg at sim. Stop (m) Y-coord. 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. 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. Following outputs are currently being extracted (more can be extracted if needed). 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 (deg.) Roll_E Vehicle’s Euler roll (deg.) Yaw Vehicle’s Euler yaw (deg.) YawLocal Vehicle’s Euler yaw offset to zero at start of simulation (deg.) Beta Sideslip angle of vehicle based on Vx and Vy (deg.) Alpha_L1 Tire L1 lateral slip (L/R is Left/Right, 1/2 is front/rare axle) (deg.) Alpha_L2 Tire L2 lateral slip (deg.) Alpha_R1 Tire R1 lateral slip (deg.) Alpha_R2 Tire R2 lateral slip (deg.) 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)

B-5 Note: At time t = 0 sec, 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 second and should be ignored. 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.

Next: APPENDIX C. SIMULATION OUTCOMES »
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Run-off-road traffic crashes account for almost one-third of the deaths and serious injuries each year on U.S. highways.

The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 296: Guidelines for Cost-Effective Safety Treatments of Roadside Ditches provides new proposed design guidance for the configuration of ditches adjacent to the roadway.

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