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Advocates of higher speed limits are distorting the facts about road deaths

By Tony Healy - posted Tuesday, 4 November 2003

Alan Buckingham's condemnation of speed cameras relies on several distortions of crash statistics, artfully draped over a long-standing polemic advanced by speed advocates in the UK, Canada and America.

The worst distortion is the claim that speeding causes only seven per cent of crashes, which he derives from research by the UK Transport Research Laboratory. To arrive at this figure, Buckingham excludes crashes assigned to more explicit categories, such as slippery roads, aggressive driving, close following and weather. Of the Australian research, by the NSW Roads and Traffic Authority, Buckingham excludes causes such as jack-knifing, excessive speed for conditions, alcohol and fatigue.

However crashes in those more explicit categories are caused, enabled or exacerbated by speed, and will be neutralised by action against speeding. Jack-knifing, for example, typically occurs when a speeding truck fails to negotiate a turn and hits a ditch or embankment. Slippery roads and weather only become a problem if speed is too high. Aggressive driving frequently means tailgating, which is a favourite activity of the speedster.


It is entirely appropriate to include those precise categories in the aggregate figure for speed. The proportion of crashes caused by speed is not the small seven per cent claimed by Buckingham, but the 30 to 40 percent claimed by road safety experts.

Why crashes are biassed towards lower speeds

Buckingham's second claim is that speeding is safer because crashes predominantly occur at extremes of low and high speeds. This confuses crash speed with sustained travelling speed, and also ignores the distorting contribution of victim vehicles.

Reported speeds in crash incidents will always be biassed towards low speeds because crashes typically occur when one vehicle is entering or leaving the traffic stream, and thus travelling more slowly or even stopped. In such circumstances, the speed of the victim vehicle will contribute to the weighting towards slower speeds that Buckingham comments on, even though the victim vehicle did not cause the crash.

As well, aggressor vehicles usually brake before impact, reducing the impact speed and extent of damage to the victim vehicle, which is often used to estimate pre-crash travelling speed. It's also worth bearing in mind that, when they're interviewed by crash investigators, speeding drivers lie.

Buckingham also attempts to use the lower crash rates on freeways as an argument that speeding is safer. This ignores the fact that freeways are designed to be safer than suburban and rural roads. Freeways are specifically designed to exclude unexpected events such as sudden side entries, vehicles manouvering at low speed, people walking, cyclists and children appearing with little or no warning.

It is thus not valid to conclude, as Buckingham does, that speeding is safer. The TRL research that Buckingham refers to actually makes this point, and Buckingham acknowledges it in his formal paper in the Centre for Independent Studies journal, but not in the articles he wrote for high-circulation newspapers. This is curious. The TRL research specifically finds that, when entry/exit crashes are excluded, and road quality is controlled for, speeding causes more crashes.


Invalidation of this argument also invalidates a related claim by speed lobbyists - that crashes result from a difference between travelling speeds, with the implication that lawful drivers are responsible for this difference. The fact is that low travelling speeds do not correlate with a higher crash rate, and that speed differences arise from the unlawful behaviour of speedsters, not lawful drivers.

Third, experience in America contradicts Buckingham's thesis. When several western states increased speed limits on long distance roads in 1996, fatality rates on those roads rose 15 percent according to the respected Insurance Institute for Highway Safety. Texas increased speed limits even on simple 2-lane roads, and suffered a staggering 45 percent increase in fatalities on those roads, according to an article by Dana Milbank in the 23 September 1997 edition of the Wall Street Journal.

Speed advocates quibble about these figures, since whole-of-state figures in America continued to decline as part of the generalised long-standing decline in crash figures. The point is that the National Highway Transport and Safety Board specifically monitored the roads where speed limits were raised, and crash rates rose on those roads.

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About the Author

Tony Healy is a research software engineer and also a policy researcher with Aus-Innovate.

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Related Links
Centre for INdependent Studies
Insurance Institute of Highway Safety
Monash University Accident Research Centre
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