CE 635 Highway Safety Lecture #1 The Problem 1

Probabilistic Risk Assessment

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ITE “crash clock” NHTSA’s TRAFFIC SAFETY FACTS ANNUAL REPORT, where you can find:TRAFFIC SAFETY FACTS ANNUAL REPORT – NHTSA’s Traffic safety facts (2006 data – final edition) 222 pp.Traffic safety facts – 2006 Traffic Safety Facts Data Summary Booklet (FARS and GES) 36 pp Traffic Safety Facts Data Summary Booklet NHTSA’s TRAFFIC SAFETY FACT SHEETS, where you can find:TRAFFIC SAFETY FACT SHEETS – Traffic Safety Facts (2007 Data Overview) 12 pp. Traffic Safety Facts (2007 Data Overview) Iowa Trends Iowa safety facts Motor Vehicle Traffic Crash Fatality Counts and Estimates of People Injured for 2006 (see long term trend graphs) Motor Vehicle Traffic Crash Fatality Counts and Estimates of People Injured for 2006

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International road safety comparisons

Hauer Philosophy You can learn the effect of a safety treatment with before and after observation? You have to have true randomized experiments to learn anything? You can learn from experience? You must take great care in doing so? You shouldn’t experiment? “the only way to find out what will happen when a complex system is disturbed is to disturb the system, not merely to observe it passively” – Box 1966

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Hauer Philosophy Opportunities abound If we do evaluate, we do so “in-house” because there is risk of failure? We do not publish because the measure failed? What is needed … – Sound methodologies – Collective will to employ them properly

Hauer quotes “Perhaps we transportation engineers can not act in good faith as the custodian of traffic safety because the goal of safety and efficiency are too often in conflict” “Within limits, highway traffic engineers can make roads safer or less safe so we must know the safety repercussions of our choices”

Road Safety Defined (From a Science- based Perspective) Improved “security” may decrease “safety” Accident or crash? Is safety the number of crashes per time? What if some days have no crashes – perfectly safe? – Use running average? – Use longer period of time? – Safety may change – must be allowed to – Requires use of statistics (expected values) and reliability during a specific period – Counts are a “hint” at the underlying numbers

Federal Transportation Goals Safety – Old: reduce fatality rate to 1.0 – New: ??? Congestion Preservation Environment How does safety interact?

Evans’ thoughts “Factors” rather than single “cause” (contributing circumstances) Is it safer to keep a pet crocodile than a pet dog?

How might these data have changed???

Human Factors

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41 Speeding Why the EZ pass speed is 15 mph Courtesy Jon Fricker, Purdue Univ.

NCHRP 500 – aggressive driving – unlicensed drivers – seat belts – Drowsy/distracted – Alcohol

How would you fill out the crash form?