Dr. Ezra Hauer, one of the world’s most respected road safety scientists, presented “Crash causation and prevention” in a webinar for the International Co-operation on Theories and Concepts in Traffic safety (ICTCT) on October 16, 2020.
He was introduced by host Dr. Stijn Daniels, President of the ICTCT Steering Committee and Director of the Knowledge Centre at the Vias institute in Brussels, Belgium.
Clinical crash causation studies (CCS) consistently find that in the majority of crashes the road user is the cause. All studies find similar results: 65% of all crashes have the road user as the sole cause, and 95% have the road user as a cause.
However, Hauer questions the definition of crash cause used in the CCS that lead to these conclusions. The CCS adopted the legal definition of cause. In law an action is ‘cause’ if, “but-for” that action, the harm would not have occurred. In the CCS a circumstance or action was considered a crash cause if “but-for” it the crash would not have occurred. But the purpose of law is not crash prevention and the purpose of prevention is not the determination of guilt or liability.
This difference of purpose renders the legal definition of cause unsuitable for crash prevention. Almost no circumstance or action occurring minutes before the crash can pass the “but-for” test, but what the road user did or didn’t do seconds before the crash will almost always pass it. This is why, Hauer asserts, that the 65%-95% is a consequence of an unsuitable cause definition, not a finding.
According to Hauer the cause of a crash “is a circumstance or action which, had it been different, the probability of such crashes to occur and/or their severity distribution would be different.” By this definition:
- Most crashes have multiple causes;
- Actions and circumstances not present at the crash time and site are also causes;
- Compliance with norms does not remove a circumstance or action from being a cause:
- While the “but-for” definition of cause supports the outmoded user-centered style safety management, the suggested definition supports the modern Safe-Systems style.
In closing, Dr. Hauer referenced a recent paper which is the basis for his presentation. “Crash causation and prevention” published in Accident Analysis & Prevention, Volume 143, August 2020, https://doi.org/10.1016/j.aap.2020.105528. He offers to provide the paper upon request through ResearchGate.
The webinar was followed by Q & A.
Watch the videorecording of Dr. Ezra Hauer’s seminar “Crash causation and prevention.”
Dr. Ezra Hauer is Professor Emeritus in the Department of Civil Engineering at the University of Toronto, Canada. He has been active in road safety research and consulting since 1970. He completed his bachelor’s and master’s degrees in Israel, and later received his doctorate from the University of California, Berkeley.
Ezra Hauer has gained a strong international reputation for his scientific rigour and practical understanding in the study of the relationship between roadway design and safety. In addition to developing new statistical methods and theories, he has excelled in translating statistical theory into techniques useful for practicing engineers and researchers alike. His books, Observational Before-After Studies in Road Safety (Pergamon 1997) and The Art of Regression Modelling in Road Safety (Springer 2015), provide invaluable guidance to the research community as well as to transportation professionals.
About the International Co-operation on Theories and Concepts in Traffic safety (ICTCT)
The International Co-operation on Theories and Concepts in Traffic safety—ICTCT—is an international association aiming since 1988 at building up and sharing scientific knowledge on road safety, with a particular interest for methods that do not only rely on crash data but also on non-crash events. It does so by organizing conferences, courses and opportunities for knowledge transfer, all directed to a worldwide professional audience. ICTCT approaches safety as an integral part of the wider road traffic system, envisaging all transport modes with a specific emphasis on vulnerable road users. https://www.ictct.net/