22 Sep 2008.
For immediate release.

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Press Release

Drivers` Group Slams Ludicrous Claims For Speed Limiters
The recently published report on ISA (Intelligent Speed Adaptation) is condemned by the Association of British Drivers for making exaggerated and unsupportable claims for potential accident reductions if speed limiters were fitted to all vehicles.
These claims are based solely on discredited theoretical relationships between average speeds and accident frequency, which the ABD has shown to be derived from studies that used dubious data manipulation and statistical techniques 1.
The ISA report 2 claims that fatalities could be reduced by 42% compared with current levels if ISA were installed in all vehicles in mandatory (non-overrideable) form, thus preventing drivers from exceeding speed limits. The claimed reductions for serious and slight accidents are 38% and 23% respectively. In 2006, however, the Department for Transport published a report 3 showing that exceeding a speed limit was a factor (not necessarily the only or main one) in just 12% of fatal, 7% of serious and 4% of slight accidents.
ABD spokesman Nigel Humphries comments:
"It should be obvious that speed limiters could not possibly prevent more accidents than those in which exceeding the speed limit is currently a factor, and in reality they would prevent fewer accidents, as other factors are involved in most cases."
There are also dangers from partial removal of vehicle control from a driver, which the ISA report glosses over. Simulator trials with mandatory ISA showed that overtaking was made more hazardous, as drivers were not able to pass quickly. Previous simulator trials 4 had shown that drivers were more inclined to tailgate, run red traffic lights and drive too fast on foggy motorways than without ISA.
The ABD believes that ISA could also encourage 'foot to the floor' driving and have the effect of diminishing the essential ability to drive to the prevailing road conditions, which often dictate a lower speed than the limit.
Field trials in modified cars only looked at changes in driver behaviour with an ISA system that could be overriden at will 5. Since the greatest accident reduction claims for ISA are in mandatory mode, it is surprising that this was not tested in the field trials. Were the researchers afraid that their claims could be undermined if accidents resulted?
The ISA report makes impressive claims for the economic benefits of ISA over a 60-year period, but these assume no other changes take place. This is clearly absurd. It is difficult enough to predict what changes might occur in the next five years, let alone sixty.
As Nigel Humphries observes:
"Other improvements in vehicles and roads will help reduce accidents, as they have done in the past. No one knows what changes will take place in the way we travel in the long term. To make economic predictions over a 60-year period confirms just how out of touch these ivory-tower academics are with reality."


1. See ABD website: Does a 1mph reduction in speed really reduce accidents by 5%? and TRL 511
2. Intelligent Speed Adaptation, Final Report
3. Contributory factors to road accidents, DfT, 2006.
4. A paper by Dr Oliver Carsten, leader of the ISA project, entitled "Can't Go, Won't Go" was presented to a government seminar on speed in 1999.
5. The car and motorcycle field trials involved volunteer, rather than randomly-selected, drivers. Their approach to ISA may not be representative, therefore, of the general population, as they are likely to have been more positively disposed to the concept beforehand. In the truck trial, the driver did not volunteer but was allocated to the test vehicle by his employer and was extremely critical of ISA, before, during and after the trial.

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