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Speed Limits

Economically Beneficial Speed Limit Increase Unreasonably Opposed 

By 18th November 2019One Comment

Sporadically politicians (typically when bolstering re-election prospects) propose increasing the archaic UK motorway speed limit to 80mph. With nowadays 50% of vehicles typically exceeding 70mph, this would be more in line with the 85th Percentile speed on UK motorways; so the 70mph limit is clearly unfit-for-purpose, urgently requiring upward revision. By correctly setting the limit using 85th Percentile principles (see Notes for Editors below), both compliance and road safety would improve.

Causation statistics show that accidents on UK motorways very seldom result from exceeding the speed limit [a reported factor in only 3% of motorway accidents; Reference 1]. Predominant contributory factors were: Driver error or reaction (76%), Injudicious action (22%), Impairment or distraction (18%), Road environment factors (11%) [Reference 2].

Our motorways are inherently very safe: 0.9 deaths and 7.64 serious injuries per billion vehicle kilometres (BnVkm). Driving the average yearly UK mileage entirely on motorways, it would respectively take some 83,000 years to cover the mileage between fatal-, and 9,800 years between serious injury accidents. Father Time will have intervened long before that…

Further, each one mph reduction in UK average traffic speed costs the economy over £1 Billion per annum in wasted productive time, due to lengthened journey times. This assertion is substantiated by a study of the effects of the recent 10kph reduction in French rural road speed limits. This generated no tangible casualty reductions; while incurring additional annual costs of over 4 Billion € in lost productive time [Reference 3]. In true Gallic fashion, public opposition to the limit reduction provoked a policy U-turn [References 4 and 5]. The substantial cost savings (from shortened journey times) far outweigh any notional economic casualty reduction benefits; which are anyway (as above) never observed practically.

Needless to say, Road Safety GB opposes increasing the motorway speed limit [Reference 6]. This is hardly surprising. The membership of this body is predominantly composed of special interest groups whose funding is, in one way or another, derived from the upward spiralling revenues generated by currently unregulated UK speed enforcement activities. Obviously, anything which would reduce these revenues would be very unpopular with them: turkeys don’t vote for Christmas, after all!

Road Safety GB’s avowed casualty reduction aspirations would be better achieved by inverting its current Pareto road safety approach (focussing 97% of its efforts on 3% of the problem, [Reference 7]). Instead, it should be advocating policies to tackle the primary contributory factors to the overwhelming 97% of road accidents that don’t involve breaking speed limits.

The ABD counsels clear-minded politicians to hold their nerve and to ensure the delivery of the economic, road safety and reduced journey stress benefits that an 80mph motorway speed limit would generate.


1. From RCGB2017 (Road Casualties Great Britain 2017) Table RAS50003, Contributory factors in road accidents by road class, Great Britain 2017.

2. Note: Factors sum to over 100% because all accidents have several, often overlapping, contributory factors.





7. “In 2016, for all [reported] accidents, 2.8% (5,157) of vehicles had an exceeding the speed limit contributory factor attributed to them. This has remained stable over the past five 5 years, with the value being 2.6% (5,645 vehicles) in 2011.” See p.15 of Vehicle Speed Compliance Statistics, Great Britain, 2017; URL:

Notes for Editors:

The 85th Percentile Principle is the speed limit setting methodology internationally accepted (by genuine road safety practitioners) to deliver the “sweet-spot” combination of optimal road safety with highest compliance.


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