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London Region

Why Accidents Don't Fall
   Road Safety

The following article was published in February 2004.

Why Accidents Donít Fall

It is puzzling to many people, that despite the massive expenditure on speed humps, speed cameras and other traffic calming measures in the last few years, accident numbers do not fall as expected.  

Road traffic fatalities in London actually rose by 20% between 1995 and 2002, and slight injuries only show a slight fall. This is despite the fact that many millions of pounds have been spent on road safety schemes in London in that period (expenditure is running at over £20 million per year in London at present). 

Itís also worth bearing in mind also that every single scheme has also been judged to show a very substantial return on investment, using calculations promoted by ROSPA and other bodies. These are based on reported historic before and after accident rates from the Molasses database maintained by local authorities. Robert Gifford of PACTS recently claimed that Local Authorities can save one life by spending £100,000 on such measures, but clearly they do not in reality. Why do the expected accident reductions disappear when wide area accident figures are examined? 

An interesting light was thrown on this in a study published in 1999 by the US Federal Highway Administration called ďResearch, Development and Implementation of Pedestrian Safety Facilities in the UKĒ. This said: ďPedestrian accidents have declined sharply over the past 5 years. However, establishing causes and effects is not easy. As noted earlier, the amount of pedestrian activity had also declined sharply.

In addition, the evaluation of the accident reduction effects from specific countermeasures has rarely been rigorous, partly because of practical difficulties. The typical method consists of a comparison of reported accidents (or casualties) for 3 years before and after the scheme. It rarely includes the known confounding factors such as changes in traffic flow, changes in traffic composition (particularly pedestrian flows), background trends in accident numbers, regression to mean effects, adaptive behaviour by vulnerable road users or more controversial aspects such as accident migration. 

Elvik (1997), reviewing United Kingdom and other accident studies, found that very few allowed for these factors. He also found that when they were taken into account, little or no accident reduction benefit could be directly attributed to the countermeasure.  To compound the problem of evaluation, no work appears to have been done to show how the (claimed) accident savings from particular schemes or programs relate to the overall changes in accident numbers. 

The last two sentences have been highlighted because they are the key points. They show that the accident benefits are often a mirage.  

As a simple example of this, the ROSPA figures for the expected benefit of a road hump scheme is a reduction in accidents of 68%. However this does not take into account the actual traffic diversion which we know from other studies can be very high. In addition it ignores the other effects mentioned above, and the data is based on subjective reports by the same council staff who devised the schemes in the first place. This is not science, itís not even magic, itís just slight of hand.  

Pedestrian Accident Trends - The Truth 

Pedestrian accidents particularly demonstrate the fallacy of many road accident claims as this is one of the few areas where accidents are going down. The number of pedestrian fatalities in the UK was at a peak of 3,153 in 1966, and declined thereafter. Each year since 1990 has seen a new record low for pedestrian fatalities - in 2002 it was 775. Total pedestrian casualties have also declined substantially.  

But when pedestrian activity rates are examined, there has in fact been a similar decline (see chart above for trends in travel modes). From 1985/86 (the earliest data known) to 2002 the distance walked fell by 21%. There has been a particularly marked decline in walking by children, one of the pedestrian groups with the highest casualty rate (even more so after dark due to security concerns). In fact, according to a DETR report in 1997, they suggested that real accident rates for that group might actually be increasing! These pedestrians have often switched to using car transport, which is safer per mile travelled, if not as healthy otherwise.

So when you next hear a politician or local authority staff member claiming success for reducing child accidents by traffic calming measures, take it with a pinch of salt.

Accidental Deaths in London

Some interesting statistics were disclosed by the London Ambulance Service in their recent review of traffic calming. Apparently there are 7,500 accidental deaths a year in London, of which about 2,000 are from external causes and 5,500 from medical incidents (eg. heart attacks). However within the first 2,000 are about 300 deaths from road accidents but there are of course numerous other reasons such as falls, fires, poisonings and drowning that make up the other 1,700 (Editor: Yes itís a dangerous world).  

To put it bluntly, you are much more likely to die from other accidental causes than from a road traffic accident. This data hardly supports the contention that road deaths are extraordinarily excessive as some people have alleged, or that they can necessarily be easily reduced, as they are clearly as rare as other accidents. Obviously the weight of expenditure and effort put into reducing road accidents has to be balanced against the effort put into reducing other causes of premature death.

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