Study of under 20mph Motor Traffic Speed

[MikeF]

I came across this recent study from the University of Surrey "Traffic speeds under 20mph best for encouraging cycling to work, University of Surrey study finds"

I don't think it's been posted before, but someone, I'm sure, will say if it has.
Quite a technical study!

[Jdsk]

Very interesting. Thanks for posting.

Jonathan

[Campag]

And at a time when we face a climate emergency (with another dire report due to be published today) lower speeds also mean less fuel consumption so less CO2. And fewer casualties. Easy enough from a technical point of view of we just go fully metric and speed limits become kilometres instead of miles per hour. So, for example, 30 mph in effect becomes just under 20mph. Big effect on fuel consumption on motorways where max limit would be just under 50mph (70 kph). I can't remember the exact figures but this saves more than 25% on fuel consumption.

Will never happen of course ....

[Jdsk]

And at a time when we face a climate emergency (with another dire report due to be published today) lower speeds also mean less fuel consumption so less CO2. And fewer casualties. Easy enough from a technical point of view of we just go fully metric and speed limits become kilometres instead of miles per hour. So, for example, 30 mph in effect becomes just under 20mph. Big effect on fuel consumption on motorways where max limit would be just under 50mph (70 kph). I can't remember the exact figures but this saves more than 25% on fuel consumption.

Will never happen of course ....

But a 20 mph default limit in built-up areas is achievable. And has now started in Wales and the Borders.

https://gov.wales/introducing-20mph-speed-limits
https://www.scotborders.gov.uk/news/art ... _in_speeds

Jonathan

PS:

"Easy enough from a technical point of view of we just go fully metric and speed limits become kilometres instead of miles per hour. "

I've never seen that before. Very clever. : - )

[thirdcrank]

Re the study, rather than than the desirability of a more widespread 20mph limit:-

I try to avoid the king's new clothes syndrome by not pretending to understand what I do not and in this study much of the jargon (technical language) and the maths are way over my head. The broad conclusion seems to be that - all other things being equal - cyclists prefer riding in slower traffic to riding in faster traffic. I hesitate to comment from personal experience because it's apparently "exceptional" ie ˃7kms, ie the study covers commutes of 2.9 - 7 km commutes. (Re my maths I'm not confident I've got the "greater than" symbol correct.) With that proviso, my observation to Grudgings et al is that, traffic fumes aside, there's little gives more pleasure than riding past miles of traffic stuck in congestion.

[foxyrider]

And at a time when we face a climate emergency (with another dire report due to be published today) lower speeds also mean less fuel consumption so less CO2. And fewer casualties. Easy enough from a technical point of view of we just go fully metric and speed limits become kilometres instead of miles per hour. So, for example, 30 mph in effect becomes just under 20mph. Big effect on fuel consumption on motorways where max limit would be just under 50mph (70 kph). I can't remember the exact figures but this saves more than 25% on fuel consumption.

Will never happen of course ....

But a 20 mph default limit in built-up areas is achievable. And has now started in Wales and the Borders.

https://gov.wales/introducing-20mph-speed-limits
https://www.scotborders.gov.uk/news/art ... _in_speeds

Jonathan

PS:

"Easy enough from a technical point of view of we just go fully metric and speed limits become kilometres instead of miles per hour. "

I've never seen that before. Very clever. : - )

I made this suggestion on a previous road speed/safety discussion on here, its so simple but of course the petrolhead society that is encouraged by the gov't and media would never accept anything so simple, especially after Brexit!

[RickH]

And at a time when we face a climate emergency (with another dire report due to be published today) lower speeds also mean less fuel consumption so less CO2. And fewer casualties. Easy enough from a technical point of view of we just go fully metric and speed limits become kilometres instead of miles per hour. So, for example, 30 mph in effect becomes just under 20mph. Big effect on fuel consumption on motorways where max limit would be just under 50mph (70 kph). I can't remember the exact figures but this saves more than 25% on fuel consumption.

Will never happen of course ....

Whilst speeds of 20mph or less would definitely make things safer, I'm not sure there is much, if any, beneficial effect on fuel consumption. At least from my observation while driving. I find it is hard to get an instant fuel consumption figure over 20mpg at around 20mph, apart from coasting/engine braking downhill. Fuel consumption appears to reach peak economy between around 40 to 60 before starting to drop off above 60. (Always assuming there is some degree of accuracy in the displayed mpg rate.)

[Tinnishill]

Update from Dumfries

https://www.bbc.co.uk/news/uk-scotland- ... d-60602355

[Richard Fairhurst]

"It found that in terms of reducing traffic speed through the town the mean speed at a range of sites had been cut by about 2mph. In the majority of areas surveyed, however, that remained above the new 20mph limit."

I wish people would get away from this fixation with judging the effectiveness of 20mph limits by mean speeds. It's not the mean speed that's the problem, it's the outliers.

We got a 20mph limit in Charlbury town centre a couple of years ago. The biggest effect has been that the people who used to do 40mph in a 30mph limit now do 30mph in a 20mph limit.

That is a massive improvement. We all know the statistics that at 40mph there's a 90% likelihood that a pedestrian will be killed, whereas at 30mph it's just 20%. I'm less concerned about whether the mean speed has dropped from 24mph to 22mph - that's not the point.

[thirdcrank]

Scottish Borders 20mph limit study

viewtopic.php?p=1589437#p1589437

That's the thread about the Scottish Borders experiment (?) and I think both the experiment and that thread are still current.

This thread is about a different study

[Jdsk]

Update from Dumfries

https://www.bbc.co.uk/news/uk-scotland- ... d-60602355

Thanks for posting that.

Here's the report:
https://dumfriesgalloway.moderngov.co.u ... _Final.pdf

I've read it once, and I recommend it. But it would be a lot easier to follow if the observations were structured as in a typical scientific paper, and the Council framing and recommendations were separate.

Jonathan

[Jdsk]

"It found that in terms of reducing traffic speed through the town the mean speed at a range of sites had been cut by about 2mph. In the majority of areas surveyed, however, that remained above the new 20mph limit."

I wish people would get away from this fixation with judging the effectiveness of 20mph limits by mean speeds. It's not the mean speed that's the problem, it's the outliers.

We got a 20mph limit in Charlbury town centre a couple of years ago. The biggest effect has been that the people who used to do 40mph in a 30mph limit now do 30mph in a 20mph limit.

That is a massive improvement. We all know the statistics that at 40mph there's a 90% likelihood that a pedestrian will be killed, whereas at 30mph it's just 20%. I'm less concerned about whether the mean speed has dropped from 24mph to 22mph - that's not the point.

That's a good example of my complaint above. The report should include the raw data to allow anyone to answer that type of question.

Jonathan

[Airsporter1st]

And at a time when we face a climate emergency (with another dire report due to be published today) lower speeds also mean less fuel consumption so less CO2. And fewer casualties. Easy enough from a technical point of view of we just go fully metric and speed limits become kilometres instead of miles per hour. So, for example, 30 mph in effect becomes just under 20mph. Big effect on fuel consumption on motorways where max limit would be just under 50mph (70 kph). I can't remember the exact figures but this saves more than 25% on fuel consumption.

Will never happen of course ....

Whilst speeds of 20mph or less would definitely make things safer, I'm not sure there is much, if any, beneficial effect on fuel consumption. At least from my observation while driving. I find it is hard to get an instant fuel consumption figure over 20mpg at around 20mph, apart from coasting/engine braking downhill. Fuel consumption appears to reach peak economy between around 40 to 60 before starting to drop off above 60. (Always assuming there is some degree of accuracy in the displayed mpg rate.)

I would imagine that if lower speeds became the norm, i.c. cars would begin be tuned for greater efficiency at those speeds.

[foxyrider]

And at a time when we face a climate emergency (with another dire report due to be published today) lower speeds also mean less fuel consumption so less CO2. And fewer casualties. Easy enough from a technical point of view of we just go fully metric and speed limits become kilometres instead of miles per hour. So, for example, 30 mph in effect becomes just under 20mph. Big effect on fuel consumption on motorways where max limit would be just under 50mph (70 kph). I can't remember the exact figures but this saves more than 25% on fuel consumption.

Will never happen of course ....

Whilst speeds of 20mph or less would definitely make things safer, I'm not sure there is much, if any, beneficial effect on fuel consumption. At least from my observation while driving. I find it is hard to get an instant fuel consumption figure over 20mpg at around 20mph, apart from coasting/engine braking downhill. Fuel consumption appears to reach peak economy between around 40 to 60 before starting to drop off above 60. (Always assuming there is some degree of accuracy in the displayed mpg rate.)

I would imagine that if lower speeds became the norm, i.c. cars would begin be tuned for greater efficiency at those speeds.

Of course, with all these electric vehicles, you only need a loop in the road to enforce the limits rigidly but of course that won't happen as it takes peoples right to ignore limits away!

[xerxes]

Whilst speeds of 20mph or less would definitely make things safer, I'm not sure there is much, if any, beneficial effect on fuel consumption.

20mph actually increases fuel consumption, because in lower gears the car's engine is running faster. I am against 20mph limits for this reason. It would be far better to have stricter enforcement of the 30mph limit, and more severe penalties for breaking it, e.g. an automatic ban.