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Session #4, Forrest Council, Slides

Session #4, Forrest Council, Slides. The Potential Impacts of a Towaway Reporting Threshold on Driver/User and Roadway Safety Programs. Forrest M. Council Senior Research Scientist UNC Highway Safety Research Center. Information from Two Studies.

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Session #4, Forrest Council, Slides

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  1. Session #4, Forrest Council, Slides

  2. The Potential Impacts of a Towaway Reporting Threshold on Driver/User andRoadway Safety Programs Forrest M. Council Senior Research Scientist UNC Highway Safety Research Center

  3. Information from Two Studies • “Effects of a Towaway Reporting Threshold on Crash Analysis Results,” (Zegeer, et al., TRR 1635, 1998) • “A Review Of The Impacts Of The Towaway Reporting Threshold On North Carolina’s Highway Safety Program,” (Lacy, et al., 2001) • Both conducted under FHWA’s Highway Safety Information System (HSIS) Project

  4. Why HSIS Interest? • HSIS is a multi-year, multi-state data system (1985-present) • Crash, roadway inventory, traffic, supplemental files • Annual files from CA, IL, ME, (MI), MN, OH, NC, UT, WA • Data used by FHWA and provided to many other national research projects • www.hsrc.unc.edu/hsis/ or through FHWA site • Any change in threshold will affect HSIS data • A primary goal of HSIS is to improve safety data

  5. The two studies analyze two basic issues • What is the general effect on key crash variables used in driver, vehicle and roadway research if one moves to a towaway threshold? • Are there specific effects on the roadway-related analysis programs conducted by state and local roadway agencies? • Identification of “Sites with Promise” (i.e., high-hazard locations) • Site-specific analysis of crash patterns to define most appropriate treatment

  6. Methods • “General Effects” study • Compare crash frequencies for towaway vs. current PDO level in four HSIS states (IL, MN, MI, NC) • Examine “what’s lost” by roadway type, crash type, object struck, vehicle type • Redevelop crash prediction model using only towaway crashes

  7. Methods (con’t) • “Site-Analysis Effects” study (NC data) • Compare “high crash location” rankings based on PDO and then towaway • Compare crash patterns on collision diagrams • Questionnaire to safety engineers who used both thresholds in developing collision diagrams

  8. Results – Percent Crashes “Lost”

  9. Percent Crashes “Lost” by Roadway Class

  10. PERCENT OF TOWAWAY CRASHES BY ACCIDENT TYPE 100.0% 90.0% 80.0% 70.0% 60.0% IL-Towaway MI-Towaway 50.0% MN-Towaway PERCENT NC-Towaway 40.0% 30.0% 20.0% 10.0% 0.0% Animal Bicyclist Pedestrian/ Rollover Run-off-road/ Angle/Turning Parking/Backing Sideswipe Same Rear-end/ Run-off-road fixed object Head-on/ Opposite Dir. ACCIDENT TYPE

  11. PERCENT TOWAWAY BY FIXED OBJECT 100.0% 90.0% 80.0% 70.0% 60.0% 50.0% PERCENT IL-Towaway MI-Towaway 40.0% MN-Towaway 30.0% NC-Towaway 20.0% 10.0% 0.0% Sign Tree Fence Mailbox Guardrail Median barrier Streetlight, utility pole Ditch, embankment FIXED OBJECT

  12. PERCENT TOWAWAY BY VEHICLE TYPE 100.0% 90.0% 80.0% 70.0% 60.0% PERCENT 50.0% IL-Towaway 40.0% MI-Towaway MN-Towaway 30.0% NC-Towaway 20.0% 10.0% 0.0% Van Bus Pickup truck Passenger car Single unit truck Farm equipment Truck tractor trailer Motorcycle/ moped VEHICLE TYPE

  13. CRASH RATES FOR TOWAWAY VS. TOTAL CRASHES URBAN ROAD CLASSES 8.73 9 8 7 5.77 5.75 6 5.41 4.8 4.78 5 3.94 CRASH RATE (Crashes per 1.61 million vehicle km) 4 3.66 3.56 2.79 2.71 3 2.61 2.49 2.34 2.09 2.02 2.01 1.82 1.77 1.73 1.69 2 1.62 1.57 1.49 1.34 1.1 1.04 0.87 0.77 0.59 1 0.65 0.36 0 IL MI MN NC IL MI MN NC IL MI MN NC IL MI MN NC Urban Freeways Urban Divided Multi-lane Urban Undivided Multi-lane Urban Two-lane Total Towaway

  14. Results – Model Comparisons • Model predicting crashes/mi on rural multilane roads (MN data) • Original Poisson model for total reported crashes • New model for towaway crashes only • Not much difference • Predicted frequencies were lower (of course) • Access Control became non-significant predictor • Difference in old and new frequencies much greater for non-principal municipal arterials than for other classes

  15. Results – “Site Analyses” • Ranking of high crash locations (based on three warrants) • 50% of “top 200” intersections and 50% of “top 200” sections changed • Significant shuffling of ranking within the list (only 4 intersections and 3 sections retained same ranking) • Does it matter? (See later Miller study)

  16. Results – “Site Analysis” • Collision diagrams • 14 (7 pairs) of diagrams produced and presented in random order • 12 experienced DOT safety engineers circled “definable patterns” and starred those that were “serious and potentially treatable” • (Note that approximately 1/3 of crashes “lost” with towaway threshold)

  17. Results – “Site Analysis” (con’t) • Collision diagrams • Patterns identified decreased by 35% (247 vs. 160) • Serious patterns decreased by 41% (126 vs. 75) • Crash patterns identified changed • “Turning” patterns decreased 43% • Rear-end/swipe patterns decreased 67% • Thus, countermeasures chosen would both decrease and change • Note that other states may “lose” more crashes and patterns

  18. Results – Other Studies • Miller, et al., “Sensitivity of a Highway Safety Resource Allocation Model to Variations in Benefit Computation Parameters,” TRR 1124, 1987. • For higher safety improvement budget ($1.2 - $1.5 mill), 20-30 percent of program benefits could be lost by less reporting, among other factors • Pfefer and Raub, “Economic Analysis of Highway Safety Data – Final Report,” FHWA, 1995. • Since officer is on the scene for other duties, cost of reporting PDO crash could be as low as $20

  19. Conclusions • Move to towaway threshold will significantly affect safety data • High loses of some crash types which will affect driver, vehicle and roadway problem identification • Major changes to “HAL” rankings – how much effect? • Significant loss of site-based crash patterns • Can’t we improve efficiency by other means, such as new technology? • Is the loss of the data worth the relatively low cost of collecting it?

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