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Cutting speed limits in towns would increase pollution rather than slow traffic, according to research for a Scottish carbonreduction group.
However, the study also found that lower speeds reduced crashes and noise, and made roads more attractive for walkers and cyclists.
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Sounds like the work to "be unveiled ... next week" is the report which was actually published last September?
http://robedwards.typepad.com/files/ecci---speed-limits---2020-group-2012.pdf
Amongst other details it showed that for petrol engines the biggest change in emissions with a strict 20mph limit in town would be a 22.6% reduction in NOx, with a 1% increase in CO2 per car-km.
"with a 1% increase in CO2 per car-km"
So it's true then.
Forget all the benefits - fewer/less serious collisions/'accidents'/injuries etc.
And the possibility that a few more people may walk/cycle (more) and reduce the number of vehicles emitting anything.
It is funny how vehicle emissions suddenly become vitally important whenever it comes down to allowing them to be driven faster isn't it?
And as chdot points out. 1% increase in CO2 emissions, but then more people find walking and cycling a viable and pleasant alternative. So all you need is a 2% reduction in the number of cars on that route and the CO2 emissions go down overall.
Short-sighted doesn't even begin to describe the arguments against this - and as Min says, it's really just any excuse to be allowed to drive more quickly.
Without having read the report, it's hard to comment, but the logic behind reducing speed limits is that it causes more acceleration / deceleration due to "stop / start" driving. Personally I think this is a load of complete cobblers because;
A/ if you lower the speed limit, you have a lower speed to accelerate to and a lower speed to decelerate from, therefore you will be doing LESS acceleration and deceleration if you are driving between 0 and 20mph than between 0 and 30mph.
B/ the stop/start nature of city driving is caused not by the speed limit as much as traffic signals and other vehicles ("traffic"). Changing the speed limit will not make there be any more or less traffic signals to stop for or more or less traffic to be stuck in (although, in an ideal world there would be less as some people might realise they're better off on a bike or a bus)
I assume the IAM will be campaigning for a "40s plenty" limit outside schools to reduce vehicle emissions?
22.6% reduction in NOx
This alone is worth fighting for, let alone the increased safety for cyclists, pedestrians and other drivers that 20mph limits entail.
A bit of the Scotsman version of the report might be true, but it wouldn't be true to suggest that lower speed limits increases all forms of pollution from all sorts of cars. And the benefits of 22.6% less NOx sounds as if it might outweigh the disadvantage of 1% more CO2 per car-km, even before taking into account likely reductions in car-km, or changes in driving style that could reduce fuel consumption/ emissions even more.
The emissions-vs-speed graph on p7 of the report linked to by slowcoach makes it pretty obvious that IC-engined vehicles in a city are going to be pretty hopeless from an emissions point of view.
Noise reduction is another benefit of lower speeds which seems to be overlooked a lot (mentioned in the report naturally).
"Over the past decade the proportion of cars breaking the speed limit has declined on most roads"
but...
"The average speed [in Portsmouth] has dropped by just 1.3mph"
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