Speed limit to reduce pollution?

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Sat 22 Jun 2019 12:35
Speed limit to reduce pollution? - RichT54

Driving south down the A331 (Blackwater Valley Route) this morning I noticed that 50mph signs had appeared on the section between the Frimley Junction and the Coleford Bridge Junction (used to be 70mph).

I remembered reading that this was being planned, not to counter accidents, but to reduce air pollution.

https://www.getsurrey.co.uk/news/surrey-news/a331-speed-limit-reduced-pollution-16201298

I didn't see any fixed or mobile speed cameras and the way that everybody was flashing past me at 70+ either they hadn't seen the new signs or were just ignoring them.

I suppose the theory is that vehicles travelling more than 50mph produce more pollution, but on the other hand they are in a particular section of road for less time. I wonder if the sums really add up or if this is another case of car-hating politicians and bureaucrats wanting to give motorists a hard time?

Either way, I suspect this sort of thing will become more common in the future.

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Sat 22 Jun 2019 13:21
Speed limit to reduce pollution? - Engineer Andy

Speed reductions are often put into place because of a prevalence of accidents and/or complaints from locals who use junctions when they cannot use them safely because of the speed of oncoming vehicles on the main road.

This very issue is currently under discussion with my local council for a similar road in North Herts (A505) because of the issues: the problem is very serious - several major crashes at least once a month, my guess with one or two deaths a year, at least, just at one junction, never mind all the rest on that road.

Gatso type speed cameras were installed some years ago (70mph) and achieved nothing. Pollution can be reduced when speed limits of 70 are reduced to lower speeds, but a) only if those speeds are still reasonabl, and b) enforce by average speed camera and not spot speed cameras.

A great example of what NOT to do is the idiotic reduction (many years ago now) from 60 or 70mph to 40 or even 30 on the A41 'Watford Way' near to the split with the A1 in North London - a 50 limit enforced by average speed cameras would've been far more sensible, as half the vehicles obey the limit, but the other half don't with many barreling along at 70 and then planting on the anchors as they pass the speed cameras. Such people also aggressively tailgate.

I do think that road needed a speed reduction as the traffic in the 1980s grew hugely, as there are (and still) many small road junctions to 30mph side streets coming off the dual/three lane carriageway with no or minimal slip-offs.

I'm wondering if the same applies to the OP's road, or whether a local councillor or two lives nearby and wants the pollution and mainly noise reduced by lowering the speed limit, as well as gaining more revenue from speeding fines.

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Sat 22 Jun 2019 13:24
Speed limit to reduce pollution? - daveyjp
www.bbc.co.uk/news/uk-wales-48723302
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Sat 22 Jun 2019 13:35
Speed limit to reduce pollution? - concrete

Generally on busy roads, a speed reduction does increase traffic flow rate, therefore less pollution. I suppose the only sure way to monitor this is via average speed cameras. It can be frustrating though. While they are doing long stretches of motorway improvements and long stretches of 50mph are in place the result are strangely good. Increased traffic flow in busy periods, less pollution and better mpg from vehicles. Kind of makes up for the whole 5 minutes or so extra time lost!!! If you think of it, what would you do with those extra minutes anyway?

Cheers Concrete

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Sat 22 Jun 2019 14:06
Speed limit to reduce pollution? - Ethan Edwards

Average speed cameras result in traffic all travelling in close proximity at the same speed. I contend that having such close proximity is inherently dangerous.

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Sat 22 Jun 2019 14:32
Speed limit to reduce pollution? - Pica

I seem to recall them complaining about the air quality just at the end of the roadworks to make the M3 into a stupid motorway when vehicles were diverted down the blackwater relief road as the motorway was closed or too busy.

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Sat 22 Jun 2019 16:17
Speed limit to reduce pollution? - sammy1

50mph has just been announced on the M4 at Newport and Port Talbot for pollution levels which is the new buzz word. Strangely enough both stretches have been subject to 50 or less for years speed cameras enforcing it. With Newport speed limit is variable often going down to an enforced 30 crawl. The Newport M4 worked much better with average speed cameras through the stretch. The plain truth is that the M4 is over capacitated at peak times like the rest of the country.

I agree that we must try and reduce traffic pollution and would think that moving traffic is less polluting that crawling. 50mph if moving is OK with me

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Sat 22 Jun 2019 19:30
Speed limit to reduce pollution? - Engineer Andy

Average speed cameras result in traffic all travelling in close proximity at the same speed. I contend that having such close proximity is inherently dangerous.

Average speed cameras don't do that - poor driving does. I would contend that I've seen just as much of that on stretches of road (especially motorways) without speed cameras of any kind or when ordinary 'spot' cameras are used.

The difference being that people are driving significanlty faster and thus the slightest drop in speed ahead, especially from cars with their cruise control engaged or where their mind wanders, meaning people have to brake more sharply because they are driving too close for their speed, leading to a concertina effect, which often causes traffic jams despite there being no actual blockage, or worse still, a major pile-up.

If drivers gave other vehicles sufficient room in front and behaved responsibly, many speed restrictions would not be necessary.

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Fri 28 Jun 2019 16:41
Speed limit to reduce pollution? - Tester

Thanks -- was just about to write much the same! The average speed cameras do indeed make everything travel at essentially the same speed, but the separation of each car from the one in front is down to a driver's choices. For example, if it's a 50 mph limit and you are too close to the car in front for whatever reason, drop back to (say) 47 and watch the gap steadily grow, as if by magic! When the gap's a bit more than required ease back up to 50 and, hey presto! you'll settle down at the right speed with a nice gap. Simples, as they say.

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Sat 22 Jun 2019 22:07
Speed limit to reduce pollution? - Bromptonaut

Generally on busy roads, a speed reduction does increase traffic flow rate, therefore less pollution. I suppose the only sure way to monitor this is via average speed cameras. It can be frustrating though. While they are doing long stretches of motorway improvements and long stretches of 50mph are in place the result are strangely good. Increased traffic flow in busy periods, less pollution and better mpg from vehicles. Kind of makes up for the whole 5 minutes or so extra time lost!!! If you think of it, what would you do with those extra minutes anyway?

Cheers Concrete

Agree with all of this.

I live near M1/J16. Ten years ago joining at 16 and driving up to 19 was a lottery. You might cruise through in 20 minutes at 70 or spend 50% longer in multiple episodes of 'concertina' braking.

Application of a 50 limit for replacement of the central barrier followed by another for implementation off all lane running transformed it. At 50 everything ran smoothly, not even clear that there was a time loss.

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Sun 23 Jun 2019 12:56
Speed limit to reduce pollution? - Engineer Andy

I think if the variable speed limits and gantry warnings were kept up-to-date far better than they currently are, then many more people would be amenable to having those instead of blanket 40 or 50mph limits, so that any temporary limits imposed were appropriate to the conditions.

Better road management can make just as much difference as policy on speed limits. Similarly, better road layouts can also make a huge difference.

The problem on that resolution is that the upfront cost is often so high in comparison to tinkering/small measures (that rarely do anything useful) that councils and the government discount them because they'd, temporarily at least, have to ask for greater funding and would have to make a decent effort to get a technical case to justify it.

As an engineer, I know from personal experience that clients want a 100% guarantee of success at a minimal cost, which is an almost impossible feat for what often are complex problems to resolve. Sometime a simple (and thus cheap) solution works, but for road projects, if it were that simple, it would've already been done.

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Sun 23 Jun 2019 22:49
Speed limit to reduce pollution? - Andrew-T
www.bbc.co.uk/news/uk-wales-48723302

I suspect some Welsh authorities are sheltering under this slogan of cutting pollution to slap speed limits on country roads willy-nilly. I have travelled about 20 miles of the A5104 in North Wales regularly for about 15 years, and as of this month there is no unlimited road for the entire distance ** since a 50 has been slapped on the last stretch. None of it could be called 'urban' and the few inhabited sections are 30-limit anyway, so the 'pollution' excuse is just that. I suppose the main intention is to catch speeding bikers with the expensive ANPR cameras which have accompanied the new limits (and will need paying for, of course).

** correction - there is an unlimited stretch of a mostly single-lane B-road which ends my journey, where anything over about 30 is asking for trouble.

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Sat 22 Jun 2019 16:33
Speed limit to reduce pollution? - mss1tw

A331 (Blackwater Valley Route)

I hate this road - it's either 50mph in the inside lane with lorries/mimsers - or 90mph in the outside lane with the nutters.

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Sat 22 Jun 2019 17:02
Speed limit to reduce pollution? - Kekettykek

If I drive an electric car, I assume that I am exempt from these limits as I am not polluting?

Actually, I think I know the answer to that one.

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Sat 22 Jun 2019 18:28
Speed limit to reduce pollution? - Terry W

People should be very aware of that which impacts fuel consumption:

  • air resistance (drag) which varies according to speed. Less relevant in stop start traffic below 20mph, but a major influence where a high gear can be selected.
  • vehicle weight both in hilly areas and stop start traffic where greater weight will need more energy to get moving and up to speed
  • driver behaviour - accelerate hard and brake hard is going to increase consumption over anticipating road conditions and reacting early.
  • there are ineviably differences in both the efficiency of power units from different manufacturers to meet perceived and real customer demands. This may extend to tyre choices, gearing, frictional losses (4WD) and maturity of technology and software.

Both theorectical studies and real life measurement has demonstrated that when traffic density exceeds a certain level, lower constant speeds (40 or 50 mph) allows more traffic to flow than leaving it unpoliced 70mph.

Where the system seems faulty is that the limits seem to be set at a default lower level rather than revised upwards where traffic volumes allow. A similar observation would be made for average speed limits in roadworks when no-one is working!

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Sat 22 Jun 2019 19:42
Speed limit to reduce pollution? - Engineer Andy

People should be very aware of that which impacts fuel consumption:

  • air resistance (drag) which varies according to speed. Less relevant in stop start traffic below 20mph, but a major influence where a high gear can be selected.
  • vehicle weight both in hilly areas and stop start traffic where greater weight will need more energy to get moving and up to speed
  • driver behaviour - accelerate hard and brake hard is going to increase consumption over anticipating road conditions and reacting early.
  • there are ineviably differences in both the efficiency of power units from different manufacturers to meet perceived and real customer demands. This may extend to tyre choices, gearing, frictional losses (4WD) and maturity of technology and software.

Both theorectical studies and real life measurement has demonstrated that when traffic density exceeds a certain level, lower constant speeds (40 or 50 mph) allows more traffic to flow than leaving it unpoliced 70mph.

Where the system seems faulty is that the limits seem to be set at a default lower level rather than revised upwards where traffic volumes allow. A similar observation would be made for average speed limits in roadworks when no-one is working!

I would agree with much of what your saying there, alongside my recent comments above regarding the problems caused by people driving too close together for their speed.

As regards your comment about air resistance, it varies by the square of the velocity. What gear you're in has no effect on that (velocity only), but of course the gear you're in, and whether you're labouring the engine or not (i.e. whether it's in its proper rev range) makes a huge difference to the fuel efficiency at any speed.

It's often cited that its more fuel efficient to drive with the windows down up to about 40mph (obviously this will vary from vehicle to vehicle because of its shape, etc) and use the A/C only with the windows up over that, in order to provide a cooling effect (assuming the air outside is cooler than inside).

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Sat 29 Jun 2019 17:07
Speed limit to reduce pollution? - NARU

If I drive an electric car, I assume that I am exempt from these limits as I am not polluting?

Actually, I think I know the answer to that one.

Of course you're polluting! Perhaps just a bit less, and in different ways.

A large part of the airborne particles come from brakes and tyres, not just exhaust pipes.

The electricity for an electric car is generated somewhere. And even if solar or wind, there are still severe questions about the lifetime carbon footprint of those generation techniques.

Plus of course the environmental footprint of the electric car - especially the batteries.

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Sat 29 Jun 2019 19:15
Speed limit to reduce pollution? - Bromptonaut

Of course you're polluting! Perhaps just a bit less, and in different ways.

Issue being addressed by these limits is in urban areas with local pollution from NOx, exhaust particulates etc. In so far as electricity is generated from fossil fuels, mostly that means gas now, then CO2 may simply be moved from one place to another. But to introduce batteries or odd questions about the carbon footprint of wind or solar looks like whataboutery.

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Sun 30 Jun 2019 00:02
Speed limit to reduce pollution? - alan1302
And even if solar or wind, there are still severe questions about the lifetime carbon footprint of those generation techniques.

What questions are those?
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Sun 23 Jun 2019 00:20
Speed limit to reduce pollution? - Andrew-T

I suppose the theory is that vehicles travelling more than 50mph produce more pollution, but on the other hand they are in a particular section of road for less time. I wonder if the sums really add up or if this is another case of car-hating politicians and bureaucrats wanting to give motorists a hard time?

There's some odd logic here. It is known that vehicles use more fuel per mile at high speed than at a lower speed, mostly because of wind and rolling resistance. Therefore for any given journey from A to B, not only will more fuel be consumed at a higher speed, but the greater exhaust products will be emitted in a shorter time. A double whammy.

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Sun 23 Jun 2019 12:17
Speed limit to reduce pollution? - SteVee

I drove down the A331 last Friday and noticed the extension of the 50 MPH limit south of the Camberley turn off. I thought they would do the whole stretch down to the A31 Hogs Back - especially considering the 300k budget - how does adding a few signs cost 300K ?

Coming back North along the same stretch on Friday, I noticed that there were no 50MPH signs just before Coleford Bridge - but there are repeater signs before Frimley. all somewhat confusing.

The A331 (BVRR) is a great piece of road construction - it could easily have become a flood risk but the engineering seems to have been carefully considered and I've never had a problem with flooding. although the junction with the M3 can have some big puddles. The A331 is a very great improvement over the A325 from M3 J4 to Farnham.

I do wonder if the new 50MPH limit going North will improve the behaviour of traffic around the M3 junction as traffic would completely ignore the old 50 MPH limit at the Camberley slip. I guess it won't be long before 50MPH limits appear on the M3 J4A to J3 (both directions)

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Thu 27 Jun 2019 23:46
Speed limit to reduce pollution? - Bilboman

On holiday in Germany many years ago I passed through a few "Lärmschutz" 80 km/h signs on some stretches of motorway, notably those lying in areas governed by the Green party. It was amazing to see drivers behind and ahead of me (more than one Porsche included) slowing right down to 80 to reduce noise, which is also a form of pollution, let's not forget!

As for enforcing speed reduction in areas where it is truly needed, I would first reduce posted speed in stages (70, 60, 50 etc.) and then place a couple of real speed cameras (disguised) and a couple of dummy ones (painted bright yellow). Anyone caught speeding within the 50 zone (i.e with a heavy right foot before or after the actual "radar") gets fined and is basically without a defence. Can anyone see a problem with that?

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Sat 29 Jun 2019 13:06
Speed limit to reduce pollution? - RichT54

Coming back North along the same stretch on Friday, I noticed that there were no 50MPH signs just before Coleford Bridge - but there are repeater signs before Frimley. all somewhat confusing.

I noticed today that the 50mph signs have now appeared on the northbound section from Coleford Bridge. Still very few cars sticking to the limit however.

The A331 (BVRR) is a great piece of road construction - it could easily have become a flood risk but the engineering seems to have been carefully considered and I've never had a problem with flooding. although the junction with the M3 can have some big puddles. The A331 is a very great improvement over the A325 from M3 J4 to Farnham.

I agree, although when they opened the section from North Camp to the A31 they had used some sort of 'special' road surface material (can't remember what it was supposed to do). It was very smooth at first, but very quickly started to break up and they had to resurface it.

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Sat 29 Jun 2019 21:22
Speed limit to reduce pollution? - Glaikit Wee Scunner {P}

M1, 4 lanes, through Sheffield area, both ways, has a 60mph limit when pollution reaches a limit.

The traffic flows fine and my mpg gets even better.

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Wed 10 Jul 2019 21:40
Speed limit to reduce pollution? - BBBB

Hopefully & verybsoon we will see a blanket 40mph speed limit on ALL roads currently restricted to 50/60mph. How quickly we forget that most of the UK's road system was at one time fine for slow tiny cars & commercial vehicles using a very narrow road system. Vehicles are now wider & faster, there are too many of them on an increasingly overcrowded island, drivers are intolerant & impatient so forcing down speed by limits is inevitable. Eventually every road & every vehicle will be monitored 24/7/365 for speed so enjoy whatever speed you can now for soon it will be too late.

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