Leonard Evans President, Science Serving Society President-Emeritus, International Traffic Medicine Association (ITMA) Bloomfield Hills, Michigan USA What we do not know, hardly know, and really know about traffic safety

Summarizes what science has taught about traffic safety

do not know Start with What we do not know, hardly know, and really know about traffic safety

Members of public have a confident answer Safety researchers will likely claim reliable quantification from Grand Rapids study How does consuming alcohol affect a driver’s risk of crashing?

Grand Rapids study provided best answer to question: If a driver is observed with given BAC, what is his crash risk compared to crash risk of alcohol-free driver? Established clearly that drunk drivers’ crash risk >> sober drivers’ crash risk But -- drunk driving is illegal People who break one law are likely to break others (speeding, running red lights, etc.) Therefore, drunks, when sober, have higher crash risks than other sober drivers

Grand Rapids study therefore measures two effects combined I do not know any rigorous, or even not so rigorous, way to seperate components 1. Effect of consuming alcohol on crash risk 2. Higher crash risks of drunk drivers even when they are sober

 Obtain large sample of alcohol-free drivers  Measure average crash risk  Administer alcohol  Measure how crash risk changes Never going to happen! Only way to get rigorous answer is to conduct experiment My conclusion – consuming alcohol increases crash risk – but not as steeply as Borkenstein relationships

How does speed affect a driver’s risk of crashing? Many members of public have a confident answer Safety researchers will likely claim reliable quantification from -

Effects of speed 1. Risk of crashing increases with increasing travel speed 2. If crash occurs, risk of injury increases with increasing speed 3. If injury occurs, risk that it is fatal increases with travel speed 1% increase in travel speed increases the risk of a fatal crash by at least 4%

hardly know

(42+4)% from 1986 paper, FARS Unlikely to be improved, as required: Effectiveness of safety belts in preventing driver fatalities  Very large numbers of crashed cars with driver and passenger, at least one killed  Comparable percents of wearers and non- wearers  No belt-wearing law - “Dead men tell no lies”

Speed Belt wearing Drunk driving Benefits only relevant occupant Affects all road usersAffects all road users, although victim is usually the drunk driver (plus similarly drunk passengers) Affects ALL road users – is central

know

“More efficient brakes on an automobile will not in themselves make driving the automobile any safer.” A Theoretical Field-Analysis of Automobile Driving, American Journal of Psychology, July 1938 * * Complete paper available at

Claim that better brakes do not increase safety based on reason alone But is it possible to address empirically? Did not happen in 1940s 1950s 1960s 1970s 1980s then opportunity occurred!

Dramatic advance in brake technology Increases rollover risk by (39+16)% Large numbers of GM popular vehicles: 1991 MY – NONE had ABS 1992 MY – ALL had ABS Otherwise, no important differences ABS (antilock brakes)

really know

Number of annual fatalities in a country (if procedures are sound) Even more reliable are estimates of percent changes in fatalities from year to year Provides a way to compare safety progress in different countries Such comparisons offer insights into best ways to reduce harm in traffic

Because fatalities reach a maximum number, we can define a simple ratio:  Dimensionless (no units)  No arbitrary assumptions  Depends ONLY on fatalities Fatalities in a given year Maximum yearly fatalities  Plot* how this ratio varies in time after maximum is reached *on logarithm scale, and x100 to express as %

2013 value is 40% below 1972 maximum (32,719 down from 54,589)

This is 83.7% below The Netherlands’ all time high of 3,506 in 1972 The Netherlands had 570 traffic deaths in 2013 If US total had fallen by 83.7% from its high, US total in 2013 would be 8,875 (73% below 32,719 observed) More than 20,000 additional Americans are killed annually because US fails to match decline in Netherlands (+ 10 other countries)

USA disaster lies in ignoring basic scientific finding - which is:

 Vehicle factors are important USA disaster lies in ignoring basic scientific finding - which is:

 Vehicle factors are important, but less important than roadway factors USA disaster lies in ignoring basic scientific finding - which is:

 Vehicle factors are important, but less important than roadway factors  Roadway factors are important USA disaster lies in ignoring basic scientific finding - which is:

 Vehicle factors are important, but less important than roadway factors  Roadway factors are important, but less important than driver performance factors USA disaster lies in ignoring basic scientific finding - which is:

 Vehicle factors are important, but less important than roadway factors  Roadway factors are important, but less important than driver performance factors USA disaster lies in ignoring basic scientific finding - which is:  Driver performance factors are importantctors

 Vehicle factors are important, but less important than roadway factors  Roadway factors are important, but less important than driver performance factors USA disaster lies in ignoring basic scientific finding - which is:  Driver performance factors are important, but less important than driver behavior factors factors

Concluding comments  Although we may know less than we think we know, we still know far more than enough to sharply reduced traffic harm  And we know what NOT to do!