The safety problem: nature of the problem, extent (partially covered already), factors CE 552 week 4

Hauer Philosophy You can learn the effect of a safety treatment with before and after observation – wrong You have to have true randomized experiments to learn anything – wrong You can learn from experience – ok You must take great care in doing so – ok You shouldn’t experiment – wrong “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

Hauer Philosophy Opportunities abound If we do evaluate, we do so “in-house” because there is risk of failure We do not publish because the measure failed What is needed … – Sound methodologies – Collective will to employ them properly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

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

Human Factors Driver intelligence/skill ladder in car Des Moines drivers Reaction time tests Distractions docs\text_messaging_crash.mht Distracting Miss Daisy (includes risk compensation) Distracting Miss Daisy Cell phone bill; KCCI report Cell phone billKCCI report Speeding Why the EZ pass speed is 15 mph Fricker p. 307 “think about it”

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

Road Crash Factors