07 Jul 2011
...and Spain have subsequently raised speed limits since.
The big issue here is less about speed limits and more about improving the smooth flow of traffic, but UK transport policy has delivered the opposite with designer congestion measures which kills fuel economy and dramatically increases emissions.
Local authorities have been funded to keep their transport staff busy to turn urban routes into obstacle courses in the hope of putting off people from driving into towns, using deliberately narrowed roads with pointless kerb build outs, forests of signs and badly timed traffic lights, all of which have increased traffic dominance and congestion despite a real drop in traffic in urban areas, hence cancelling out any air quality or CO2 benefits of lower traffic volumes.
On motorways and trunk roads, poorly designed road junctions are the biggest cause of congestion. Its beyond belief how the Highways Agency have built new roads or improved existing roads that would cope well with high traffic volumes but fail to build or make adequate improvements to key connecting junctions. The M1/M6/A14 and J10 of the M40 are two classic examples of cut-price traffic engineering bodgery that has caused endless congestion rather than connecting major routes with fully free-flow grade separated junctions.
You don't need to be a transport expert to realise how poor junctions cause queues to extend from slips roads onto the main carriageway of motorways. In Ireland improvements to Junctions on the M50 show how important good junctions are to reducing congestion and emissions.
So speed limits are only a small part of the story, rather it is either deliberate or poor planning and engineering which is driving up emissions.
16 Jul 2011
DfT data says the 85th percentile speed on Motorways is now 79 mph. Engineers have known for decades that 85th percentile posted limits tend to produce the smoothest and safest traffic flow with the fewest accidents. Engineers and police also know the numbers painted on the signs have almost no effect on 85th percentile speeds, unless enforced rigidly 24/7 which is not practical on Motorways. Traffic safety people know that diverting traffic from A & B roads to Motorways will cut the fatality rate of those people by at least half and maybe more. The science is on our website. James C. Walker, National Motorists Association, www.motorists.org, Ann Arbor, Michigan USA (frequent visitor to Britain to see family) Also see www.abd.org.uk for more science.