Speed limits save lives.
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COST BENEFITS can result from the imposition of speed limits. This theory was presented for discussion at the Institute of Traffic Administration Conference in Leicester. Dr Clifford Sharp addressing the delegates argued that if speed limits are to be imposed on a hitherto unrestricted road, or if an existing speed limit is to be lowered, a list of possible costs and benefits can be drawn Up.
Dr Sharp, Reader Transport Economics at Leicester University, said the costs might include: Time costs of longer journeys; Cost of enforcement; Cost of public education campaigns; Lost profits of sports car manufacturers. The main benefits, would probably he: Reduction in accident rates; Reduced vehicle operating 3osts; Savings in fuel consump:ion; Reduction in environmen:al costs; Reduction in road onstruction costs; Reduction in
iehicle manufacturing costs. . According to Dr Sharp, some irivers, motorists organisations even Chief Constables dis)Lite the link between speed and 3ccident reduction. ''l believe," le said, -that there is very ;trong evidence to show that owering speed limits reduces iccident rates."'
The reasons why there are ewer accidents at lower speeds ;aid Dr Sharp, are: greater ireaking distance and reaction ime distance; people underesimate speeds more at higher evels; they overestimate disances more the greater they In addition, he said, that iedestrians use shorter time inervals to cross roads as the peed of vehicles increases; rivers are more prone to drive Do close to the driver in front at igher speeds; tyre grip dereases as travelling speed inreases; the kinetic energy of ehicle increases with square of le speed.
Referring to the oil-crisis Deed restrictions of 1973/74, e said: "There can be little oubt that the reduction in Deed limits led to a fall in accident rates."' During the same period, the accident rate on motorways fell from a predicted level of 0.127 to an observed figure of 0.073. According to Dr Sharp, reported accidents in the period November 1973-October 1974 fell, compared with the previous year, by 16 per cent on motorways, 15 per cent on allpurpose roads with a former speed limit of 50-70 mph and by only six per cent on allpurpose roads not affected by the speed limit reduction. In the same period in the whole country, there was a three per cent fall in traffic flow and a 10 per cent drop in accidents. In the US, fatal accidents fell by 27 per cent and injury accidents by 24 per cent on controlled access roads on which the speed limit was reduced from 65 to 55 mph. A study of accidents in California suggested that about 40 per cent of the fall in the accident rate could be attributed to the more stringent speed restrictions.
The pre-fuel crisis speed limit of 70 mph was restored for motorways in Britain by March 29, 1974, and for all-purpose roads on May 8, 1974. A new restriction for all-purpose roads of 50 mph on single carriageways and 60 mph on dual carriageways was introduced on December 14, 1974, but this was replaced by a limit of 60 mph on single and 70 mph on dual carriageways on June 1.
Although the relationship between speed limits and accidents is complicated, it is quite clear that the speed limit reductions in 1973-4 did reduce accident rates. People alive today would have been killed if speed limits had not been reduced. Many more would have suffered in injury accidents.
But this reduction in what many people would regard as the most serious disbenefit produced by road transport was obtained only as a by-product of a decision motivated by the desire to use fuel more sparingly and to protect Britain's balance of payments position.
"It is really the case that the speed limit reductions were justified by the balance of payments considerations but would not have been justified by the
accident reductions alone? ( it perhaps that the State react to a danger to the baIE of payments in a way thicannot react to a threat to safety of its citizens?" askei Sharp, and went on:
"Is the planned returr pre-fuel crisis speed limits, that we have more of our owl supplies available, in the pu interest?
"If the trade-off between duced journey times and probability of being involve, a road accident could presented clearly for public cussion and decision, we there be a majority in favou the higher speed limits?
-Is this, perhaps, an a where the benefits of she journey times can easily be ceived, while the costs may be appreciated by people v have not studied accid statistics?"
Dr Sharp said that, given the sts of fuel, the estimated mey costs of road casualties d the estimated values of time rings, it is possible to estimate ptimum" speed limits.
"Thus, Ghosh, Lees and Seal culated that, if the TR R L esiates of the cost of accidents re used and time valued at E1 hour and a 'unit of casualty' £244.34, the optimum speed motorways would be 67.45 Ai. Reducing time values to ip per hour would reduce the timum speed to 47.69 mph, t doubling the cost of a casuy would only reduce the opium speed with time at £1.00 hour to 62.30mph.
"This raises the question of lether estimates of the cost of )d accidents are of the right der of magnitude when opnum speeds are shown to be ore sensitive to changes .in no values than to those in acdent costs. Estimated accident .sts in Britain are increased to low for observed rates of inition (indicated by changes in
e Retail Price Index) and real owth."
'Time-saving values are reted to earnings. This would iggest that, when earnings rise ster than the inflation rates, -ne savings values would inease more than accident costs -id, therefore, speed limits iould be raised, and vice versa. is appears to be an area in
which any mechanical projection of figures may lead to unpredicted and possibly perverse results.
Dr Sharp said we should consider some of the absurdities and inconsistencies surrounding speed limits. Motoring correspondents still talk about top speeds of 120mph when this is meaningless in most countries. We also need to put different accident reduction measures into perspective and should not spend a great deal of resources on methods which will have little result. He instanced the British Rail campaign for more goods traffic.
"In Railtalk," he said, "they have used knocking copy which would bring a blush to the cheeks of the most hardened detergent manufacturer when asking his advertisers to say rde things about 'Brand X', -According to Naritalk, 'For any given haul a heavy lorry is 12 to 17 times more likely to cause a fatal accident and 35 to 50 times more likely to cause serious injury than the equivalent rail movement.'
"This contains two extremely misleading statements. Of course, lorries in a mixed traffic flow are more likely to be involved in accidents than the goods trains, but it is just not true that the lorry is necessarily to blame for the accident, as the word cause suggests.