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

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Using the HSIP Five Percent Report

• Is my location a “5%” site?– Map– Illinois Roadway Information System

(IRIS) location

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Five Percent Reporting

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PSI = 152 Fixed Object and Overturn = 51% Rear End and Same

Direction Sideswipe = 35%

Five Percent Reporting

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Driving too fast for conditions = 45%

Listing of Crashes

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06-0698

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

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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)

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Quantitative Site Analysis

• Is this intersection performing poorly?

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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

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Quantitative Site Analysis

• Is this intersection performing poorly?

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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.

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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

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Thank youDave.Piper@illinois.gov

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