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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 Sun, 6 May 2018 - 16:55
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original links?


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notmeatloaf
post Sun, 6 May 2018 - 19:24
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https://www.eea.europa.eu/themes/transport/speed-limits
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The Rookie
post Sun, 6 May 2018 - 19:59
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Those numbers don’t tally with the ones I have from test cars.


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notmeatloaf
post Mon, 7 May 2018 - 15:34
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So I guess it is a choice.

A clearly well researched article by an organisation with the expertise and funds to carry it out.

Or you, and some numbers you remember but can't find anywhere online to cite.

For me, I have never seen any figures that remotely tally with what you say.
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The Rookie
post Mon, 7 May 2018 - 18:28
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You can’t find them online as they are my companies cars being tested out our expense for our internal work. We wouldn’t put the results online funnily enough!

I’ve been emissions testing cars on chassis dyno’s since 1989, it was then my day job (apart from a few breaks) until 2006, in the 18 months before that I was running an average of 3 cars a day, 5 days a week.


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notmeatloaf
post Mon, 7 May 2018 - 19:09
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Indeed, but you'd think someone, anyone, would have done public research with a graph showing the same thing? After all, driving faster = less pollution is what everyone wants to hear.

It doesn't make sense from a car manufacturer point of view to me because we all know they are desperate (and indeed with VW too desperate) to pass the emissions tests, and clearly the mean/median speed for those is around that crucial 35-50mph point.

To make them more efficient in some way at 70mph would be a significant feat because if you worked in this field you will be used to seeing

P = (½ρCAv)cubed

Basically, if you double speed then air resistance quadruples. So if if requires 5kw of engine power to overcome air resistance at 35mph, you need 20kw of power just to overcome air resistance at 70mph, which of course comes from your fuel.

As a cyclist you don't need a formula to tell you that anyway, at high speeds most of your energy is just going to overcome air resistance and it is very difficult to accelerate.

I'm not disbelieving you did these tests, I just struggle to see how you could have got the result you did.

This post has been edited by notmeatloaf: Mon, 7 May 2018 - 19:10
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Tartarus
post Tue, 8 May 2018 - 09:45
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So from the graphs, it's basically saying that as you travel faster, diesel cars put out less CO and more NOx, and petrol cars put out less NOx and more CO? It does tally with the Government's early 2000s policy of pushing diesel because they were only focussed on COx emissions at the time, and the dangers of NOx were not being looked at.
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The Rookie
post Tue, 8 May 2018 - 11:43
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QUOTE (notmeatloaf @ Mon, 7 May 2018 - 20:09) *
To make them more efficient in some way at 70mph would be a significant feat because if you worked in this field you will be used to seeing

P = (½ρCAv)cubed

Efficiency (energy content of fuel and how to use it) and combustion and after treatment efficiency are totally unrelated, relevant to CO2, not to CO, HC, NOx or particlulates.


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Redivi
post Tue, 8 May 2018 - 12:07
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P = (½ρCAv)cubed

Basically, if you double speed then air resistance quadruples. So if if requires 5kw of engine power to overcome air resistance at 35mph, you need 20kw of power just to overcome air resistance at 70mph, which of course comes from your fuel.


Completely agree that the engine output is unrelated to the pollution measurements

Regarding the power required, it's worse than that

Air resistance is proportional to the velocity squared but Power is Resistance x Speed
If you double the speed, the power required is cubed so 5 kw at 35 mph needs 40 kw at 70 mph

Not ideal speeds to compare because tyre resistance and transmission losses are proportional to speed and, for a car at 35 mph will be a significant fraction of the total losses

A car at 35 mph is also either in a lower gear (= higher transmission losses) or operating in an inefficient part of its rev range

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notmeatloaf
post Tue, 8 May 2018 - 12:31
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QUOTE (The Rookie @ Tue, 8 May 2018 - 12:43) *
Efficiency (energy content of fuel and how to use it) and combustion and after treatment efficiency are totally unrelated, relevant to CO2, not to CO, HC, NOx or particlulates.

Indeed, which is why it's important to have well designed studies.

You know that with science results have to be replicable to be considered reliable. The issue is that apparently no-one has replicated your results, but plenty have replicated results showing the exact opposite. That's probably why government policy seems to be that reducing the speed limit from 70mph to 50mph reduces pollution, because it's evidence based rather than just to troll everyone.
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The Rookie
post Tue, 8 May 2018 - 13:00
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My opinion is based on evidence, evidence from hundreds of hours testing, you?


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notmeatloaf
post Tue, 8 May 2018 - 19:57
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Mine is based on evidence that exists on the internet in the form of peer reviewed studies.

Yours is based on evidence in your head and apparently nowhere else.

This post has been edited by notmeatloaf: Tue, 8 May 2018 - 19:59
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southpaw82
post Tue, 8 May 2018 - 20:04
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Do you two want to get a room or something?


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