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Uses ofSafety Performance
Functionsand
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, 2009 2
Using the HSIP Five Percent Report
• Is my location a “5%” site?– Map– Illinois Roadway Information System
(IRIS) location
July 29 and 30, 2009 3
Five Percent Reporting
July 29 and 30, 2009 4
PSI = 152 Fixed Object and Overturn = 51% Rear End and Same
Direction Sideswipe = 35%
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, 2009 8
Quantitative Site Analysis
• Is this intersection performing poorly?
9
Thru AADT = 2575Stop AADT = 2650Experience = 7 crashes in 5 years. (‘04 – ‘08)1.4 crashes per year1 Fatal CrashRecent PDO crash in 12/08, and A-Injury crash in 01/09
HSM: N spf 4ST = exp[-8.56 + 0.60xln(AADT maj ) + 0.61xln(AADTmin)]= 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, 2009 10
Quantitative Site Analysis
• Is this intersection performing poorly?
July 29 and 30, 200911
Thru AADT = 2300Stop AADT = 650Experience = 10 crashes in 5 years. (‘04 – ‘08)2.0 crashes per year1 Fatal Crash3 A-Injury Crashes2B-Injury Crashes
HSM: N spf 4ST = exp[-8.56 + 0.60xln(AADT maj ) + 0.61xln(AADTmin)]= 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, 2009 12
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, 2009 13