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Reducing speed to cut emissions

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On 23 September 2013, the Telegraph reported that the government had “not stopped work” on the idea of raising Britain’s motorway speed limit to 80 mph. Now, it is consulting on cutting pollution by setting a 60 mph maximum ‘for a number of years’ on a 32-mile stretch of the M1, from junction 28 near Matlock, to junction 35a north of Rotherham (BBC News).

The speed restriction could be applied from 7am to 7pm every day of the week, but other options under consideration include peak-hours-only, Mondays to Fridays only, or imposing the limit on a shorter stretch of road.

[Justin Parkinson, Political reporter, BBC News, 6 Jan 2014]

[The RAC] warned that reducing the maximum speed from the national standard 70mph to 60mph could “pave the way for similar restrictions on other sections of motorway” and there would “inevitably be a negative impact on business efficiency and individual mobility”.

[… The RAC’s technical director David Bizley said]: “More worryingly, it could pave the way for similar restrictions on other sections of motorway. While preserving air quality is obviously a paramount concern there will inevitably be a negative impact on business efficiency and individual mobility.

“This very powerfully demonstrates the impact that speed has on emissions and many will be surprised to hear that a reduction of just 10mph can have such a significant effect on improving air quality.”

In most cars, fuel consumption is substantially higher at 70 mph compared to 55 mph, so there would be carbon reduction from an effective 60 mph limit. Air quality would be dependent on the mix as well as the volume of vehicles using the motorway; large HGVs, all of which are diesel powered, are already restricted to 60 mph on motorways.

A lower motorway speed limit should mean reduced stopping distances, so it’s plausible that there would be capacity advantages (in the much same way that a 150 mph railway has a shorter safe train spacing distance than a 250 mph one). It seems likely that the phenomenon of phantom jams is exacerbated with higher road speeds.

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Written by beleben

January 7, 2014 at 11:45 am

Posted in High speed rail, Politics

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