According to an article in the UK’s Daily Mail on the 13th June (see here), the British government has plans to increase the speed limit on motorways from 70 mile/hr to 80 mile/hr (from 112 km/hr to 128 km/hr).
The article says that ” raising the limit to 80mph is still firmly on the Government’s agenda” and that “there will be three trials of the higher speeds in different areas, and if successful they will be introduced across the country”. A former transport secretary, Philip Hammond, argued that “raising the limit could ‘provide hundreds of millions of pounds for the economy’, generated by lowering journey times”.
Road safety charity Brake (website) opposes the plans, arguing an 80mph limit is likely to ‘lead to more deaths, crashes and serious injuries’. There is even an organisation dedicated to opposing the plans to raise the speed limit. This “No to 80” organisation’s supporters include Greenpeace and the Campaign for Better Transport.
I tend to suspect that the concept of cost savings from lowering journey times has little merit. In the real world for example, any two minutes saved by driving more quickly will likely be spent watching football on TV rather than on any productive activity.
But I also wonder about valid trials, and about the effect on engineering design theory. For example, road engineers measure road surface friction, apply a factor of safety to the observed values, and use them in calculating horizontal road radius, stopping sight distance and so on, as related to a specific design speed.
What happens if, after the road has been designed and built, someone says “OK, we designed for 70 but let’s now increase the permitted speed to 80” ? – (or is the engineering theory so crude that it has very large factors of safety built into it).
To be perhaps cynical, any planned trials should be made on sections of motorway which have a bad accident record. This will likely lead to more statistically robust test results. The opposite approach, such as testing on a straight, level section of motorway with a good road surface during a dry summer could automatically lead to a “no accidents before, no accidents after” situation.