Changes to UK speed limits

Transport Secretary Philip Hammond is expected to announce the move at the Conservative party conference in Manchester this weekend.  And it would seen as a victory for Hammond over Cabinet sceptics Chris Huhne and Andrew Lansley.  Energy Secretary Huhne is concerned the change will be bad for the environment as drivers burn more fuel, and Health Secretary Lansley is known to have argued that there will be an increase in road deaths and accidents as a result.

The policy is part of Tory plans to win the “Top Gear vote” after accusations that Labour had launched a “war on the motorist”.  Hammond believes the move will boost British business by cutting journey times.  But the new limit may only apply in England and Wales, with Scotland’s staying at 70mph.  Such a situation would lead to chaos at the Border with England where the M6 crosses into Scotland!

Environmental groups make the straightforward point that driving at 80mph uses more fuel – anything up to 25% – than at 70mph, with a resultant effect on emissions.  “If instead you cut the speed limit to 60mph you could save as much as 7 megatonnes of carbon a year. Even enforcing the speed limit would save up to a megatonne,” Friends of the Earth said.

Motoring groups gave a cautious response to the plans. Professor Stephen Glaister, director of the RAC Foundation, said: “Drivers travelling that 10mph quicker might reach their destination sooner, but will use about 20% more fuel and emit 20% more CO2. There is also likely to be a slight increase in road casualties. And what about enforcement? If police follow existing guidelines, many people could do 90mph before action is taken.  Before you change a speed limit, you have to know whether you are doing it for safety, economic or environmental reasons. Unfortunately not all of these are compatible.”

Ironically in congested conditions a lower speed limit might actually speed up journey times.  Under the Highways Agency Managed Motorways scheme variable speed limits are in force on several stretches of motorway.  The idea is that a lower limit actually calms and smooths traffic flow, removing the bunching and stop-start motoring that occurs when there is a free-for-all.

Businesses value predictability of journeys rather than duration and HGVs will still presumably be doing 60MPH, so they won’t benefit from the higher limit.  Ironically a lot of congestion is due to collisions, a higher limit will likely mean more collisions, and collisions between faster-moving vehicles will tend to be more severe, so any economic benefits from some faster journeys may be neutralised by increased congestion, less predictable journeys and the costs of more casualties.

Even ignoring collision-related congestion, faster journeys won’t necessarily result from a higher limit. It may simply mean that drivers get to the next bottleneck quicker and spend more time queueing. That after all is why the M25 variable speed limit works – if people drive slower, they actually travel quicker. Traffic flow may suffer from the increased speed differential between vehicles – drivers wishing to pull out into another lane will have to allow a bigger gap, and drivers will need to keep a greater distance behind the car in front to be able to stop safely (something not all drivers bother much about). If the prospect of faster journeys attracts more drivers, that will mean more congestion.

What seems to have received little news is that Hammond is expected to couple the increase with an expansion of 20mph limits in many urban areas which will be popular with many cyclists.  I look forward to seeing more details on that part of his plan.

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