Reducing traffic speeds below 40mph may increase toxic pollution, says Transport Research Laboratory report

Sometimes I cycle to work and sometimes I drive a car to work.
When I drive it takes me longer to get there because of the big queues of traffic I become part of.
Despite part of the journey being in a 40 mph speed limit I never manage that speed and rarely get close to 30mph, so in my real life experience, reducing the speed limit would make absolutely no difference to the speed I'm actually able to drive at and therefore make no difference to the emissions spewed from my car.
It might just slow down some of the nutters that use the residential streets around my neighbourhood as rat-run racetracks though.
hmmmm.

PUT INNER CITY DRIVERS IN ELECTRIC CARS!!

Sedgepeat, you are wrong about lower speed limits (and a few other things besides). The reports of increased accidents in 20mph areas were based on figures that failed to take account of the larger numbers of roads which are now 20 mph. Measured by distance travelled, the areas covered by 20mph zones are safer. Not by much, but better enforcement and road design would probably sort that out.

If you read this website regularly instead of just dropping in to try and direct traffic to your appalling dog's dinner of a page, you'd be aware of this.

http://road.cc/content/news/63367-media-criticised-misleading-coverage-s...

All this misses the truth that motor vehicles keep society going and without them we would die pretty rapidly. Not at all healthy. Witness. The faster mankind got so life expectancy went up. Unfortunately the population explosion that went with it and thus the vicious circle of more people,needing more vehicles to sustain it all.

But our study, backed with results in areas that have adopted blanket 20 zones, is that accident rates have gone up in them. So no ,they're not safer for cyclists or pedestrians. This is all explained on our site www.youdrive.co and include the confession to us by the DfT & TRL that they had grossly exagerrated chid accident figures by using percentages to justify them.

Surely less speed = perceived safer roads, thus encouraging more people onto bikes and decreasing pollution?

It's appalling that the report relies on dishonesty -Comparing apples with oranges to 'prove' a falsehood is utterly disgraceful.

The answer is to keep cars out town-centres and allow only restricted access for motorised traffic.

The first benefit would be the regeneration of the high-street, which was severely damaged by the private motor-car and out of town shopping centres.
Then there would be a dramatic drop in transport-related air pollution which kills ~35,000 people per year.
Source: House of Commons Environmental Audit Committee Air Quality Fifth Report of Session 2009–10 Volume I

By excluding cars from town centres way we'd short journeys by car (with their appalling fuel-inefficiency) with bicycles which are at least 25 times as fuel-efficient.
Source: Sustainability Without the Hot Air McKay.

----

It's about time motorists paid the full costs of motoring, instead of whining about 'road-tax' and the cost of fuel and accusing cyclists of not paying their fair-share.

Each registered vehicle in the UK is subsidised by 2000 Euros per year, (on average, 2008 figures).

Source:
The True Costs of Automobility: External Costs of Cars Overview on existing estimates in EU-27
Final Report
TU Dresden
Dresden, October 12th, 2012

Just got round to watching that Poynton video, and it's very interesting stuff. Although I can't help wondering if the benefits they're waxing lyrical over are, to use As Easy As Riding A Bike's metaphor, just the result of getting the hockey players to go into the ice rink in single file. http://aseasyasridingabike.wordpress.com/2012/01/09/treating-the-symptom...

The starting point for any discussion on which road speed is the most appropriate should be this -

"Results show that the average risk of severe injury for a pedestrian struck by a vehicle reaches 10% at an impact speed of 16 mph, 25% at 23 mph, 50% at 31 mph, 75% at 39 mph, and 90% at 46 mph. The average risk of death for a pedestrian reaches 10% at an impact speed of 23 mph, 25% at 32 mph,50% at 42 mph, 75% at 50 mph, and 90% at 58 mph. Risks vary significantly by age. For example, the average risk of severe injury or death for a 70‐year‐old pedestrian struck by a car travelling at 25 mph is similar to the risk for a 30‐year‐old pedestrian struck at 35 mph." (https://www.aaafoundation.org/sites/default/files/2011PedestrianRiskVsSp...). Is an extra 10 mph really worth a 100% increase in the risk of a pedestrian being killed?

This also explains how fuel efficiency is affected by speed - http://auto.howstuffworks.com/fuel-efficiency/fuel-economy/question477.htm

the new set up in poynton is great, however if you have ever ridden through there (as many manchester readers may have on the way out to the peaks) you'll find the major failing for cyclists is that the materials used in its construction are when wet %100 lethal. I've gone down twice on that roundabout, once without realising the danger and a second time even when trying to be careful.

Nice idea but a bit of a fail in execution as far as cycling is concerned (i might add both of these accidents occurred on nearly new GP4000s tyres).

I'm always wary of studies that focus on CO2 emissions without considering the wider context. What percentage of the time do cars drive at the posted speed limit anyway? My gut feeling is that during busy periods, average speeds are well under (it's taken me an hour to drive a mile across Bristol city centre before, and that's not particularly unusual).

If more people were cycling or taking the bus, there would be fewer cars, less emissions, and average journey times would decrease. But that's not going to happen while roads are threatening places where cars rule untamed.

There may be a factr which has not been mentioned - driving at less than 30mph(51kph, not a dinosaur!) in most modern cars means using lower gear than top, so engine revs are a bit higher, this may mean the engine is running efficiently as it would around 60/70 kph in top gear, so one is balanced by another? As I run a diesel, in town I rarely go further tha 4th of 5 gears, often 3rd at 30mph in traffic. But I know from checking that a steady 113kph (70mph) on motorways is by far the most efficient at over 50/55 mpg, in a 1500kg car. Confusing, isn't it? It's acceleration and braking that uses the fuel, and a smooth driving style changes both mpg and pollution levels. Pollution = boy racers flying up to hazards and braking hard, using up pads, discs, tryres, then tearing off using loads of fuel and tyres.
Less pollution = people who can drive properly, easing into hazards and moving easily away, using hardly and brakes, tyres, and minimising fuel consumed. Which seems to be simple common sense.
Perhaps the solution is proper driver training, not just be taught to pass a once in a lifetime test?

is the result actually "there's less stop-start driving on the sort of roads that are appropriate for 40mph and higher speed limits"?

Less speed = less fuel used = less pollution.

If speed is reduced, then it will take longer to travel to your destination, which in turn will mean more time spent driving, which means more congestion, which in turn leads to even slower speeds, and more pollution.

it's always a good idea to provide a link to the original research, so that people that can read and think would be able to make their own minds up rather than follow statements from someone else.

I see that the TRL did a literature review called Traffic calming and vehicle emissions: a literature review in 1997. (payment required for download)

Have you checked the commissioned report itself? You don't seem give a link to it. I note that The Edinburgh Centre for Carbon ­Innovation is listed at Companies House. Its web site is a bit light on practical accounts of who they are and what they do for a living. I'm not suggesting one thing or another. But when I read an item about "commissioned research" I normally want to skim the data and methodology before I give it credence - especially, perhaps, when the headline seems to be counter-intuitive or controversial.

The logic of this seems to be a little flawed.

Surely Stop-Start driving in a higher speed limit area would mean more time spent accelerating to get to that higher speed.

Also emissions are linked to engine speed as higher revs lead to incomplete combustion, they needn't be linked to the travelling speed of the car. Its only gear ratios.

If the speed limits are set to keep people safe, the vehicles can easily be designed to minimise pollutants at those speeds. Road safety and environmental policy should drive vehicle design, not the other way around.

Just found a ref for the statement above, according to Professor James Curran, the chief executive of the Scottish Environment Protection Agency “Reducing speed really will reduce emissions”.

Curiously I saw a report of the same research today that said reducing speed limits would reduce air pollution (which is also supported by previous research based on monitoring air pollution while varying speed limits). I get the feeling that the story is being spun by the motoring lobby. Either way, I will find out when I go to the Edinburgh Centre for Carbon Innovation Seminar on Wednesday.

Your headline is totally wrong.

You should be asking: "Why would a 50kph (30mph for the barbarians) speed limit increase stop-and-start driving?"

And if a default 30kph speed limit in urban areas is adopted, the Government should work with the motor industry to force them to make cars run efficiently at that speed.

"The reason for the air pollution is the increased amount of acceleration and braking in stop-start driving"

And that is a MASSIVE caveat which basically means the stand-out message is complete and utter bollocks: stop-start driving increases emissions, lower speed doesn't. No surprise to anyone.

Properly controlling traffic speeds often leads to *less* "stop-start" driving - anyone who's been on a stretch of road with average speed cameras should attest to this.