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Accelerated carbon challenges with new speed limit

04 October 2011
Accelerated carbon challenges with new speed limit

By Robin Haycock, Head of Transport, The Climate Group.

October 4, 2011. 

The UK Government has proposed an 80MPH motorway speed limit. And I thought the UK had carbon targets!?

Well it is rare for me to have a negative comment about our UK Government and in particular the Department for Transport as I worked on secondment there for a couple of years, and understand the pain it is to try and achieve anything in terms of policy. But here is madness. Or is it populist? 

The list of issues that show this to be fundamentally wrong are long, but let’s look at a couple of the most important ones.

Here in the UK we have a target for reducing carbon emissions from road transport, so even the lower limit quoted by Lord Shut at 14% increase in emissions is a massive hit in terms of how we progress. Reality is that this is a constant 70mph against a constant 80mph comparison, and the nearer likelihood is 26% due to all kinds of factors, but trying to maintain this speed becomes difficult and acceleration / deceleration inevitable.

Whilst on acceleration and deceleration we come to the next point, which is that as motorway speeds increase, the capacity of the road decreases, resulting in pulsing of traffic then traffic jams.

This is contrary to the main argument made that increasing speed limits will increase productivity due to people achieving quicker journey times. Oh dear.

If the capacity of the road goes down due to the increased speed limit, then the current hotspots of congestion will increase across the country. Hmm, let me think about that one.

Let's then look at a great scheme that really works. That of the M42 motorway variable speed limits around Birmingham. This increases capacity significantly and reduces accidents and driver stress.

Increasing to 80mph only ensures we have a problem trying to enforce as before, and given that people will then drive at 90mph and above and that air resistance goes exponential with speed, we don’t really increase carbon emissions by 26%. It is a lot worse.

Cars then need to get heavier for better resistance in high speed crashes, and this increases fuel consumption again. Oh and now we get onto the value of life - which is not my specialist area.

Stay tuned for more positive news as soon as possible! 

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