Uses of Safety Performance Functions and Potential for Safety Improvement Values David L. Piper, P.E. Illinois Department of Transportation

Applications of SPF and PSI Using the HSIP Five Percent Report Safety Analysis in Phase I Quantitative Site Analysis July 29 and 30, 20092

Using the HSIP Five Percent Report Is my location a “5%” site? – Map – Illinois Roadway Information System (IRIS) location July 29 and 30, 20093

Five Percent Reporting July 29 and 30, PSI = 152 Fixed Object and Overturn = 51% Rear End and Same Direction Sideswipe = 35%

Five Percent Reporting July 29 and 30, Driving too fast for conditions = 45%

Listing of Crashes July 29 and 30,

Using SPF and PSI Information in Phase I Creation of the 5% Report requires a look at 100% of sites. Weighting of PSI supports goal to reduce K’s and A’s Substantive safety measure at project level Breakdown by segments and intersections within the project 7

Using SPF and PSI Information in Phase I Suggested triggers for Road Safety Assessment if: – PSI is 10 or higher – Segment or intersection in top 33% of its peer group – If segment or intersection has PSI 50% higher than adjacent similar location(s) July 29 and 30, 20098

Quantitative Site Analysis Is this intersection performing poorly? 9 Thru AADT = 2575 Stop AADT = 2650 Experience = 7 crashes in 5 years. (‘04 – ‘08) 1.4 crashes per year 1 Fatal Crash Recent PDO crash in 12/08, and A-Injury crash in 01/09 HSM: N spf 4ST = exp[ xln(AADT maj ) xln(AADT min )] = 2.61 crashes/year (No night crashes) IDOT SPF: N K+I = exp(-8.05)*((AADT major )^0.674)*((AADT minor )^0.272) = 0.55 K+I crashes per 5 years.

Quantitative Site Analysis Countermeasures Completed – Lighting – Improve sight distance (hedge clearing) – Relocated utility sign Countermeasures Under Consideration – Improved warning signs – Police private signs on ROW July 29 and 30,

Quantitative Site Analysis Is this intersection performing poorly? July 29 and 30, Thru AADT = 2300 Stop AADT = 650 Experience = 10 crashes in 5 years. (‘04 – ‘08) 2.0 crashes per year 1 Fatal Crash 3 A-Injury Crashes 2B-Injury Crashes HSM: N spf 4ST = exp[ xln(AADT maj ) xln(AADT min )] = 1.04 crashes/year IDOT SPF: N K+I = exp(-8.05)*((AADT major )^0.674)*((AADT minor )^0.272) = 0.34 K+I crashes per 5 years.

Quantitative Site Analysis Countermeasures Completed – Removed trees in sight triangle Countermeasures Under Consideration – Improved warning signs – Police private signs on ROW – Lighting Overall – Quantitative analysis supports actions taken, and informs future decisions. July 29 and 30,

Summary SPF/PSI Products Support – Identification of safety opportunities – IDOT goal to reduce K’s and A’s – Office review of 5% locations – Focus of resources to best effect – Credibility of analysis SPF/PSI Products will Support – SafetyAnalyst – Highway Safety Manual July 29 and 30,

Thank you July 29 and 30,