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More millions wasted, Welsh government to impose 50 speed limits on M4
Richy_m_99
post Wed, 25 Apr 2018 - 11:36
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https://www.walesonline.co.uk/news/wales-ne...limits-14572377

Welsh Government announce plans for a blanket maximum speed limit of 50 mph through Port Talbot and Newport on the M4 together with other major roads to cut down on polution.

Apart from the stupidity of thinking that slowing traffic and prolonging congestion on already congested parts of the motorway reduces polution, millions were spent on converting the motorways around Newport (between junction 24 and 28) into a "managed motorway". It took three years to complete and during the entire time the entire stretch was restricted to 50mph for the entire duration of the works. It cause massive problems, endless overnight road closures and at the end of it, all we got were a load of pretty speed signs, a few speed cameras for revenue collecting and no extra lane capacity or benefit whatsoever.

Now they want to throw the whole thing away and make the whole stretch 50mph again, (except when they want to slow it up even more). Mind you, 50 around the Brynglass tunnel approaches is often an aspiration, rarely a limit anyway.

This post has been edited by Richy_m_99: Wed, 25 Apr 2018 - 11:36
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post Wed, 25 Apr 2018 - 11:36
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The Rookie
post Wed, 25 Apr 2018 - 11:58
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I'd love for a politician to explain in actual factual terms how a car doing 50mph produces less pollution than one doing 70mph.

Its scientifically illiterate to suggest its the case, maybe they could speak to people that actually work on cars and controlling pollution to establish facts!


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Trampilot
post Wed, 25 Apr 2018 - 12:04
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I read last year that the 50mph speed limit was debunked because it created more congestion and made the roads more dangerous.

http://www.bbc.co.uk/news/uk-41704392

Highways Agency were researching it.
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DancingDad
post Wed, 25 Apr 2018 - 13:52
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QUOTE (The Rookie @ Wed, 25 Apr 2018 - 12:58) *
I'd love for a politician to explain in actual factual terms how a car doing 50mph produces less pollution than one doing 70mph..........


Based on my car, cruising in 5th, 2,500 RPM v 3,500 RPM (approx.)

Less air going in, less fuel, less pollutants coming out.

That's the simplistic.
I fully accept that will be other factors
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666
post Wed, 25 Apr 2018 - 14:43
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QUOTE (DancingDad @ Wed, 25 Apr 2018 - 14:52) *
QUOTE (The Rookie @ Wed, 25 Apr 2018 - 12:58) *
I'd love for a politician to explain in actual factual terms how a car doing 50mph produces less pollution than one doing 70mph..........


Based on my car, cruising in 5th, 2,500 RPM v 3,500 RPM (approx.)

Less air going in, less fuel, less pollutants coming out.

That's the simplistic.
I fully accept that will be other factors


Sticking with the simplistic approach (which is about as far as my brain allows):

Assuming pollution is proportional to engine speed and hence road speed, then pollution per minute is also proportional.

BUT pollution per mile, which is surely what matters, is independent of speed.
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The Rookie
post Wed, 25 Apr 2018 - 15:08
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QUOTE (DancingDad @ Wed, 25 Apr 2018 - 14:52) *
QUOTE (The Rookie @ Wed, 25 Apr 2018 - 12:58) *
I'd love for a politician to explain in actual factual terms how a car doing 50mph produces less pollution than one doing 70mph..........


Based on my car, cruising in 5th, 2,500 RPM v 3,500 RPM (approx.)

Less air going in, less fuel, less pollutants coming out.

That's the simplistic.

Simplistic and very wrong, otherwise how does a big SUV with a 5.0 litre engine aver meet the required emissions standards when it can be pretty hard getting a small car with a 1.0 to pass? I guess the politicians were as simplistic and actually getting professional advice was beyond them.

Tailpipe emissions of HC, NOx and CO2 (as well as particulates) have no correlation to speed at all until you get to much higher speeds (depending on the engine and vehicle configuration). This will have 2 parts of no effect at all on tailpipe pollution. Emissions control is my old day job (and still part of my current one), I've run thousands of emissions tests over the years.

What is a benefit is 'smart motorways' where they control traffic flow to reduce stop start and/or constant accelerating and braking.


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Redivi
post Wed, 25 Apr 2018 - 16:02
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Deleted

This post has been edited by Redivi: Thu, 26 Apr 2018 - 02:57
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Fredd
post Wed, 25 Apr 2018 - 16:19
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QUOTE (Redivi @ Wed, 25 Apr 2018 - 17:02) *
Can somebody explain, by the way, why the increased energy consumption of high speed rail travel is never an issue ?

Possibly because even high speed trains (assuming they don't have to stop and start frequently) are far more efficient in terms of energy used per passenger km than cars.


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The Rookie
post Wed, 25 Apr 2018 - 20:59
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QUOTE (Redivi @ Wed, 25 Apr 2018 - 17:02) *
Simplistic and very wrong, otherwise how does a big SUV with a 5.0 litre engine aver meet the required emissions standards when it can be pretty hard getting a small car with a 1.0 to pass?

A rather big elephant in the room

The emission standards are all concerned with pollutants per litre and ignore how many litres are passing out of the tail-pipe

No emissions regulates are grams per kilometre and measured at the tailpipe, not sure where you got that per litre stuff from but simply not true. More like a unicorn than an elephant?

https://www.theaa.com/driving-advice/fuels-...sions-standards

This post has been edited by The Rookie: Wed, 25 Apr 2018 - 21:12


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andy_foster
post Wed, 25 Apr 2018 - 21:21
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QUOTE (The Rookie @ Wed, 25 Apr 2018 - 12:58) *
Its scientifically illiterate to suggest its the case, maybe they could speak to people that actually work on cars and controlling pollution to establish facts!


It's


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Some people think that I make them feel stupid. To be fair, they deserve most of the credit.
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Redivi
post Thu, 26 Apr 2018 - 03:13
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QUOTE (The Rookie @ Wed, 25 Apr 2018 - 21:59) *
QUOTE (Redivi @ Wed, 25 Apr 2018 - 17:02) *
Simplistic and very wrong, otherwise how does a big SUV with a 5.0 litre engine aver meet the required emissions standards when it can be pretty hard getting a small car with a 1.0 to pass?

A rather big elephant in the room

The emission standards are all concerned with pollutants per litre and ignore how many litres are passing out of the tail-pipe

No emissions regulates are grams per kilometre and measured at the tailpipe, not sure where you got that per litre stuff from but simply not true. More like a unicorn than an elephant?

https://www.theaa.com/driving-advice/fuels-...sions-standards

**** deleted

Was thinking of my recent MOT test

Will be interesting to see if the Euro 6d Real Driving Emissions test produces realistic results

Found this article interesting at the time
What's your experience ?
http://www.bbc.co.uk/news/resources/idt-sh...our_car_exhaust
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The Rookie
post Thu, 26 Apr 2018 - 06:39
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I read that article when it first came out, one of my team (well ex now as he just left) at work was heavily involved with the on road testing after the VW scandal first broke, was in front of parliamentary select committees etc. Put bluntly some manufacturers take a more ethical approach than others, when you do all the mapping work on a car for emissions you can either do every speed/load site equally or they can focus on those sites that are used through the emissions test and pay lip service to the others. That is not a cheat device and not illegal.

What VW used was a ‘defeat device’ to change the settings fundamentally when the car wasn’t being used on a rolling road.

If you look at the on road data that came out (including the UK government study which my ex-colleague supported and was involved in writing the report) it’s clear that some manufacturers are playing a bit fast and loose with the spirit of the regulations and that there emissions are little better than VWs illegal cars were, others (and I’ll mention BMW as a good example) are complying with the spirit and letter of the law.

My expertise is on petrol engines cars, but I have some Diesel experience, a pre Dieselgate VW would pretty much always emit a puff of black smoke when accelerating away, I was also suspicious at how they were getting through the emissions test with that (assuming they must have been super super clean for the rest of the time), at least now I know! It also explains why their real world fuel economy was always that bit better compared to the rival manufacturers. Of course if you bought a ‘defective’ car because of that fuel economy and the low speed performance on offer you would be really miffed after the fix to find it’s now lost the edge in both respects now it’s been ‘fixed’.


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Redivi
post Wed, 2 May 2018 - 11:55
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According to a report today, Port Talbot is the worst city in the UK for fine particle air pollution at nearly double the WHO limit

http://www.bbc.co.uk/news/health-43964341

I find it hard to believe that motorway traffic is responsible or that reducing speed limits will make a significant improvement

It looks more than an exercise to demonstrate that "something is being done" than a genuine attempt to improve air quality
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The Rookie
post Thu, 3 May 2018 - 10:07
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QUOTE (Redivi @ Wed, 2 May 2018 - 12:55) *
According to a report today, Port Talbot is the worst city in the UK for fine particle air pollution at nearly double the WHO limit

http://www.bbc.co.uk/news/health-43964341

The telling bit...
QUOTE
And some of the figures - including in Port Talbot - are estimates based on measurements of larger particles of pollution.

Some large particles are nothing to do with combustion (sandy dust for example) which is what creates the vast majority of the smaller particles (and that includes wood burning stoves - http://www.bbc.co.uk/news/world-europe-39115829 ) so this can be very misleading.

When I worked in Dagenham that would have very very high large particle readings whenever the dredgers where offloading silt on dry windy days.......

This post has been edited by The Rookie: Thu, 3 May 2018 - 10:08


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DancingDad
post Thu, 3 May 2018 - 14:54
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QUOTE (Redivi @ Wed, 2 May 2018 - 12:55) *
According to a report today, Port Talbot is the worst city in the UK for fine particle air pollution at nearly double the WHO limit
...........I find it hard to believe that motorway traffic is responsible or that reducing speed limits will make a significant improvement........


And me.
Port Talbot has a relatively quiet section of the M4 going past it
And one of the biggest steel works in Europe.
Any bets on where particulates are coming from, I'll put mine on the steel works.
Spend an hour in there and your nose blows black.
Spend a day and the shower drain is black for the first five minutes.
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notmeatloaf
post Fri, 4 May 2018 - 20:11
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If you look at any speed/mpg graph for a road car the efficient speed will always be between 35mph and 50mph.

Pollution doesn't entirely follow fuel consumption but it is a good broad guide.

Also on busy roads 50mph will mean less stop/start traffic.

The theory is sound.
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Richy_m_99
post Sat, 5 May 2018 - 04:42
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And now the WHO says whoops, we got it wrong about Port Talbot.

https://www.walesonline.co.uk/news/wales-ne...s-says-14618131
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The Rookie
post Sat, 5 May 2018 - 05:25
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QUOTE (notmeatloaf @ Fri, 4 May 2018 - 21:11) *
If you look at any speed/mpg graph for a road car the efficient speed will always be between 35mph and 50mph.

Pollution doesn't entirely follow fuel consumption but it is a good broad guide.

Also on busy roads 50mph will mean less stop/start traffic.

The theory is sound.

Regulated pollutant and speed do not correlate at all, as has already been fully explained, it may make some sense to a lay person, to someone who actually knows, it’s bollocks.

So, oops, the theory is not sound.

It’s already a managed motorway as I understand, so no need for ‘stop/start traffic’ (by which you presumably actually mean constantly changing speed?) either.


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Richy_m_99
post Sun, 6 May 2018 - 01:05
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QUOTE
It’s already a managed motorway as I understand, so no need for ‘stop/start traffic’ (by which you presumably actually mean constantly changing speed?) either.



I would prefer it to be called a mismanaged motorway.

I can appreciate when the variable speed limits are correctly applied, as they seem to be on the M42 for example when they do appear to keep the traffic moving. On the Welsh section, there is often no correlation between the limit set and the volume of traffic.

Even worse is the frequent reduction in speed required past gantries with speed cameras with the next gantry, 800 yards further on with no camera displaying a significantly higher speed. Example, 50mph three miles before roadworks, 40mph a mile before, 20mph on a camera gantry on the approach to roadworks at 0400 on a Sunday morning, and 50 at the actual start of roadworks.
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notmeatloaf
post Sun, 6 May 2018 - 15:36
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QUOTE (The Rookie @ Sat, 5 May 2018 - 06:25) *
Regulated pollutant and speed do not correlate at all, as has already been fully explained, it may make some sense to a lay person, to someone who actually knows, it’s bollocks.

So, oops, the theory is not sound.

It’s already a managed motorway as I understand, so no need for ‘stop/start traffic’ (by which you presumably actually mean constantly changing speed?) either.

Graph showing that pollutants are lower at 70mph than 50mph then please, as "someone who knows"?

Certainly you have no idea of traffic modelling if you think there is less stop start traffic over the course of 24 hours with a 70mph limit vs 50mph. A computer running a scenario is much, much more accurate than what you think because you drive on a motorway sometimes.

Here's some to start you off.

Impact of travelling speed on various pollutants (Euro 4 diesel passenger cars, 1.4–2.0 litre engine capacity


Impact of travelling speed on various pollutants (Euro 4 gasoline passenger cars, 1.4–2.0 litre engine capacity)

Sources: EMISIA - ETC/ACM

This post has been edited by notmeatloaf: Sun, 6 May 2018 - 15:49
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