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Richy_m_99
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.
The Rookie
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!
Trampilot
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.
DancingDad
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
666
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.
The Rookie
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.
Redivi
Deleted
Fredd
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.
The Rookie
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
andy_foster
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
Redivi
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
The Rookie
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’.
Redivi
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
The Rookie
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.......
DancingDad
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.
notmeatloaf
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.
Richy_m_99
And now the WHO says whoops, we got it wrong about Port Talbot.

https://www.walesonline.co.uk/news/wales-ne...s-says-14618131
The Rookie
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.
Richy_m_99
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.
notmeatloaf
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
The Rookie
original links?
notmeatloaf
https://www.eea.europa.eu/themes/transport/speed-limits
The Rookie
Those numbers don’t tally with the ones I have from test cars.
notmeatloaf
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.
The Rookie
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.
notmeatloaf
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.
Tartarus
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.
The Rookie
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.
Redivi
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
notmeatloaf
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.
The Rookie
My opinion is based on evidence, evidence from hundreds of hours testing, you?
notmeatloaf
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.
southpaw82
Do you two want to get a room or something?
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