1. Highway Safety Information System (HSIS) Evaluation of Lane Reduction “Road Diet” Measures on Crashes and Injuries Herman F. Huang and Charles V. Zegeer University of North Carolina Highway Safety Research Center

2. Highway Safety Information System (HSIS) What Is a Road Diet?

3. Highway Safety Information System (HSIS) Arguello Blvd., San Francisco After Before

4. Highway Safety Information System (HSIS) Road Diet Benefits sDrivers’ speeds limited by lead vehicle sMay reduce left turn delays sPedestrians have fewer lanes of traffic to cross sSidewalks and bike lanes can be added sTurn pockets and refuge islands can be added

5. Highway Safety Information System (HSIS) Research Design  Four-group design: s Road diet - “before” s Road diet - “after” s Comparison site - “before” s Comparison site - “after” s Obtained crash data from cities  3 yrs of “before” - 3 yrs of “after” Objective To investigate the effects of road diets on motor vehicle crashes and injuries.

6. Highway Safety Information System (HSIS) Road Diet Comparison Site

7. Highway Safety Information System (HSIS) Analysis sInitially had 30 road diets and 50 comparison sites sMany locations had short lengths, small sample sizes of crashes, low ADTs sLocations used in analysis: s12 road d iets (2,068 crashes) s25 comparison sites (8,556 crashes) sThese were assigned into 11 groups

8. Highway Safety Information System (HSIS) Study Sites and Crashes Used in the Analyses

9. Highway Safety Information System (HSIS) Analysis Categories  Crash Trends to Validate Comparison Sites s “Before” and “After” Crash Frequencies s B/A Crash Rates s B/A Crash Severity s B/A Crash Type

10. Highway Safety Information System (HSIS) Crashes per Month, Oakland Analysis of the trends in Oakland and other cities showed that the comparison sites were a good match to the road diets.

11. Highway Safety Information System (HSIS) “Before” and “After” Crash Frequencies s11 road diets and 24 comparison sites sRoad diets had about 6% fewer crashes in the “after” period than the comparison sites sOverall increase in ADT - any traffic diversion is limited sADTs increased by 6.4% on road diets and 8.0% on comparison sites

12. Highway Safety Information System (HSIS) Crash Rates (per million vehicle miles) s8 road diets and 14 comparison sites sCrash rates were lower at road diets in both periods. sRegression analysis indicated no differences in road diet and comparison site rate changes in B/A.. Before After Before After Road Diets Comparison Sites

13. Highway Safety Information System (HSIS) Crash Severity s10 road diets, 20 comparison sites sAbout 63% of the crashes were PDO and 37% had at least one injury or fatality sCrash severity was virtually the same at road diets and comparison sites, and did not change from the “before” to the “after” period sInjury % varied somewhat from city to city - different crash reporting practices

14. Highway Safety Information System (HSIS) Crash Types s12 road diets and 25 comparison sites sThe changes between the “before” and “after” periods were not significant.

15. Highway Safety Information System (HSIS) Conclusions sTrend analyses indicated comparison sites were valid sRoad diets had 6% fewer crashes in the “after” period than the comparison sites sWhile crash rates were lower at road diets sites in both periods, relative change in B/A was not significant sCrash severity was the same at road diets and comparison sites and did not change in B/A  Traffic operations and capacity must be considered at each site