Polluting Motorway Speed limit may be cut to 60mph

[Bad Company]

So, no citation then - just a reference to some petrolhead's blog...

Not exactly credible, dontchathink?

I did say that I 'nicked' that bit so sorry, no cigar.

In the meantime I make no apology for 'nicking' the next bit from another petrolhead forum:-

However, if you take that spreadsheet and believe the numbers, take a look at HGV's in terms of Nox/km. Now tell me where, if you wanted to improve local air quality, where you should be focusing your attention!


(for example, if we take an average of EU2-EU6 passenger cars g/km Nox at 70mph and 60mph respectively:

Gasoline: 59mg / 56mg
Derv: 629mg / 493mg

Current uk passenger car fleet is 70% gasoline & 30% diesel so lets amalgamate those figures to:

230mg/187mg at 70 & 60mph respectivel, and so a speed limit reduction "saves" 43mg per car, per km driven

And yet, a single Eu3 (2005 onwards) HGV puts out 5233mg/km at a steady 56mpg!


So, removing a single truck is equivalent to ~122 cars slowing down by 10mph.
For a single pre-euro emissions standard truck then that is 262 cars equivalent!)



It's a bit like banning people from a shopping center because one person is smoking a cigarette, rather than asking the smoker to stop!

 

[Bad Company]

I have few rules in life, but one of them is never, ever, trust anyone who calls diesel, "Derv".....

Diesel Engine Road Vehicle .

 

[Dan B]

So, removing a single truck is equivalent to ~122 cars slowing down by 10mph.

Does it take fewer or more than 122 cars to transport everything that would otherwise be moved by that truck?

 

[theclaud]

I have few rules in life, but one of them is never, ever, trust anyone who calls diesel, "Derv".....

I believe @User will confirm that the other important one is not to alight at stations called "Parkway".

 

[subaqua]

[QUOTE 3174569, member: 45"]Studies (and your needle) suggest that fuel economy drops significantly between 50 and 70mph.

That's all you need to know.[/QUOTE]
yup, I am happy at cruising at 60mph in lane 1 , overtaking where neccesary , for max fuel economy. below that it went a bit wrong. YMMV in your car.

 

[Wobblers]

Bit of a Google came up with - http://www.diaryofanadi.co.uk/?p=14616


The minimal increase in roadload does not significantly increase Pmax, (the engine speed is higher (because you're generally already in top gear at 60) you can make the higher power requirement from the same torque (and hence the same Pmax/BMEP). At such speeds, the exhaust after treatment system will be fully working, and the actual tailpipe Nox emissions are incredibly tiny. For a typical passenger car, 85% of tailpipe emissions occur at cold start (when the after treatment system is not yet operational.

Admitedly I 'nicked' most of that partly from another forum and partly from speaking with my son who is a vehicle design engineer at a motor manufacturer. There is more which I will try to post up later.

Also the proposal does not account for somebody driving say a Tesla which can apparently reach 130 mph with no emmissions.

In other words, no.

Three way catalytic convertors work best when fuel is burned at the stoichiometric ratio [1] which happens to be the point of maximum power delivery (which probably goes some way to explaining the motor manufacturers enthusiastic adoption of them) which will see most, but not all of the nitrogen oxides removed. As long as the catalyst is up to working temperature. Or not been poisoned. Or degraded. Or coked up. Or is simply old (active surface area decreases with time as the platinum particles sinter). But they do nothing for the major pollutant - which is the fine particulates.

The amount of energy needed to move a specific distance increase with the square of the speed (because air resistance increases with the square of the speed). This means reducing speeds from 70 to 60 mph will result in one quarter reduction of emissions. Yes, this is a very crude analysis and does not take into account the various parasite loads (things like lights, pumps, all those wonderful electronic gizmos motorists just have to have) which do nothing to move the vehicle, but we're still well above the most efficient cruise speed that cars are designed for, so a substantial reduction in all pollutants can be expected.

[1] I had to spend many boring hours learning this guff, so I don't see why I should spare you!

ETA: HGVs make up a small fraction of total traffic, so it would of very limited benefit to focus on them to the exclusion of all else. Further, speed reductions will also act to reduce their emissions too.

 

[albion]

Ken tells it like it is though that cheap touch of blue paint might have won it for Boris..

http://www.theguardian.com/commenti...on-thousands-london-dying-prematurely-drivers

"Two years later, in 2010, the government's medical advisers updated their analysis of London's air quality with the shocking conclusion that 4,300 Londoners died prematurely each year – by an average of 11 and a half years."
"In the Chinese city of Shenzen, 3,000 electric buses are already working on their streets. London does not have one."

 

[Bad Company]

"In the Chinese city of Shenzen, 3,000 electric buses are already working on their streets. London does not have one."

Where does the electricity come from?

 

[albion]

Coal, Hydro and then Wind.

Their use of nuclear is becoming more negligible, the risks no doubt being deemed too high.

 

[Dan B]

Where does the electricity come from?

Bankers on treadmills