1. Low Cost Safety Improvements Pooled Funds Study Safety of Lane/Shoulder Width Combinations on Two-Lane Rural Roads Dr. Frank Gross, Vanasse Hangen Brustlin (VHB), Inc Dr. Paul P. Jovanis, Penn State University

2. Overview u Introduction u Objective u Study Design u Methodology u Data Collection u Preliminary Results u Conclusions u Future Research

3. Background on Strategy u Shoulder Paving/Widening l Proven strategy u Pavement Width l What lane/shoulder width produces lowest crash odds? l Identified at Technical Advisory Committee June 2006 u Target crashes l Head-on l Run-off-road l Sideswipe u Potential Difficulties l Confounding Variables u Key to Success l Flexible modeling approach

4. Literature Review u Crash Modification Factors in Highway Safety Manual l Key studies: Zegeer et al. (1981); Zegeer et al. (1988); Griffin and Mak (1987) Recommended CMF for Shoulder Width (Harwood et al., 2000)

5. Literature Review u Few Studies Address Allocation of Total Width l “Road diets” change total number of lanes Burden and Lagerwey (2001); Welch (1999) l Reallocation of width on urban freeways Add lane by reducing lane and shoulder width McCasland (1978); Urbanik and Bonilla (1987) u Evaluate Re-allocation Without Other Changes

6. Objective u Estimate Safety Effectiveness l For a given pavement width, what allocation of lane/shoulder width produces the lowest crash odds? u Secondary Questions of Interest l Do effects vary by: Traffic volume? Speed limit? l For a given lane width, do effects vary as shoulder width increases? l Is the treatment economically feasible?

7. Methodology u Case-Control Methodology l Cases: crash-involved segments for a given year l Controls: non-crash-involved segments for a given year u Matching Variables l ADT and Segment Length u Additional Covariates l Speed, District, Unpaved Shoulder, Curvature, and Grade

8. Methodology PairADT Segment length SW: 0 SW: 1 SW: 2 SW: 3 SW: 4 SW: 5 LW: 9 LW: 10 LW:1 1 LW:1 2 Outcome 12500100001001 12500000100010 24310000010001 24301000001000 SW means shoulder width and LW means lane width

9. Methodology u Case-Control Methodology l Allows answer to primary and secondary questions l Regression-to-the-mean not an issue l Accounts for confounding variables Matched design Model covariates

10. Study Design u Required Sample Size l Minimum: 15,094 segment-years Detect 10 percent reduction in total crashes with 90 percent confidence l Desirable: 57,576 segment-years Detect 5 percent reduction in total crashes with 90 percent confidence u Assumption l 50 percent discordant pairs u How Does Assumption Hold? l PA discordant pairs: 70 percent (LW) and 80 percent (SW) l WA discordant pairs: 66 percent (LW) and 84 percent (SW)

11. Data Collection-1

12. Data Collection-2 u Crash Data l 5 years of PA data l 6 years of WA data u Roadway Data (PA and WA) l Number of Lanes l Area Type l AADT l Segment Length l Speed Limit l Surface Width l Paved Shoulder Width (WA only) l Horizontal Curvature l Vertical Curvature (PA only) l Unpaved Shoulder Width l District

13. Data Collection-3 Variable PA Cases (total crashes) PA Controls (total crashes) WA Cases (total crashes) WA Controls (total crashes) PA Cases (target crashes) PA Controls (target crashes) WA Cases (target crashes) WA Controls (target crashes) Length (ft)25982578193618742628260920591996 AADT39213701469343983530336341333970 Speed (mph) 47.3648.2051.0451.1847.6148.2651.7651.65 Lane Width (ft) 11.2111.1911.5511.6111.0211.1011.4911.61 Shoulder Width (ft) 2.963.144.955.232.823.024.815.33

14. Data Collection -4 Pavement Width Lane Width Shoulder Width PA Sample (Total crashes) WA Sample (Total crashes) PA Sample (Target crashes) WA Sample (Target crashes) 26' 10‘3'4,8383523,55060 26' 11'2'4,4432,0013,134522 26' 12'1'19617314853 28' 10'4'4,0242252,80320 28' 11'3'6,7562,5814,601686 28' 12'2'1,485591994161 30' 10'5'5678439317 30' 11'4'10,1562,3886,622526 30' 12'3'2,1561,4791,420429 32' 10'6'4066325012 32' 11'5'2,9607781,932206 32' 12'4'4,8592,3583,107640 34' 10'7'844541 34' 11'6'2,6771,1901,667277 34' 12'5'1,242906720242 36' 10'8'75614214 36' 11'7'294403188115 36' 12'6'1,5771,691954454 Total 48,79517,32832,5794,435

15. Evaluation Results (PA Total Crashes) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 101112 Lane Width Category (ft) Crash Risk 26' PW 32' PW 36' PW 34' PW 30' PW 28' PW

16. Evaluation Results (PA Target Crashes) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 101112 Lane Width Category (ft) Crash Risk 26' PW 32' PW 36' PW 34' PW 30' PW 28' PW

17. Evaluation Results (WA Total Crashes) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 101112 Lane Width Category (ft) Crash Risk 26' PW 32' PW 36' PW 34' PW 30' PW 28' PW

18. Evaluation Results (WA Target Crashes) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 101112 Lane Width Category (ft) Crash Risk 26' PW 32' PW 36' PW 34' PW 30' PW 28' PW

19. Example Odds Ratio Total Paved Width (ft) LW (ft) SW (ft) Odds Ratio Standard Error P value Lower Confidence Level. Lower Confidence Level 32 1061.000**** 32 1151.4190.1970.0121.0811.863 32 1241.3660.1850.0211.0471.783

20. Conclusions u Within Pavement Width l PA: Not many significant changes Particularly for total crashes l WA: General decrease in crashes for narrow lane and wide shoulder Target crashes in particular Be aware of small samples u Within Lane Width l General decrease in crashes as shoulder increases Supports model results (consistent with prior studies) u Preliminary Results! l Need to explore outliers l Answer secondary questions

21. Future Research u Field-verify sites in PA l Preliminary data verification using PA video logs u Evaluate Anomalies l Met with PennDOT to discuss results l Review PennDOT and WSDOT design guides u Secondary Questions l Do effects vary by: Traffic volumes? Speed limit? u Economic analysis

22. QUESTIONS or COMMENTS