Lower motorway speed limits
Discussion
aw51 121565 said:
I doubt this particular situation (the proposed M1 scheme) would happen on autoroutes in France, for example, where the population is more spread out and the average population density countrywide is only around 25% that of the UK 
.
It's simple then, the solution is a cull. .obob said:
dcb said:
+1
It's only a consultation.
Clearly some trees are more important than getting from A to B safely and efficiently.
Even if the authorities are daft enough to implement it, will the police
bother to enforce it ?
Average speed cameras are on most of that stretchIt's only a consultation.
Clearly some trees are more important than getting from A to B safely and efficiently.
Even if the authorities are daft enough to implement it, will the police
bother to enforce it ?
dcb said:
+1
It's only a consultation.
Clearly some trees are more important than getting from A to B safely and efficiently.
Even if the authorities are daft enough to implement it, will the police
bother to enforce it ?
(My bold) Huh? I appreciate you don't agree with being made to drive slower, as you want to get there faster. But I don't see how you could argue that driving at 60, rather than 70, would be anything other than safer AND more efficient?It's only a consultation.
Clearly some trees are more important than getting from A to B safely and efficiently.
Even if the authorities are daft enough to implement it, will the police
bother to enforce it ?
(Note, I didn't say "significantly", but it will no doubt be just a bit safer at 60 than 70, and it will be more efficient. Unless you have a car which is more efficient at 70 than 60, but I think that would be out of the norm.)
"This very powerfully demonstrates the impact that speed has on emissions and many will be surprised to hear that a reduction of just 10mph can have such a significant effect on improving air quality."
er, fail!
For modern passenger cars, the nox increase in moving between a steady speed of 70mph and 60mph is almost immeasurably small at the tailpipe!
(this is because 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).
The "Pollution" will actually be coming from large diesel trucks and busses, which are not doing 70mph!
er, fail!
For modern passenger cars, the nox increase in moving between a steady speed of 70mph and 60mph is almost immeasurably small at the tailpipe!
(this is because 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).
The "Pollution" will actually be coming from large diesel trucks and busses, which are not doing 70mph!
Matthen said:
They do this on the Auto-routes - on a temporary, as needed basis.
Also in Switzerland. When weather conditions lend themselves to trapping emissions, the limit is reduced on some stretches from 120kmh to 80kmh. There's an indicator next to the motorway I drive every day telling you what the air quality is like. The speed limit was reduced to 80 for a couple of weeks last year/year before iirc. Luckily I was on holiday at the time and missed most of it. 
mrmr96 said:
(My bold) Huh? I appreciate you don't agree with being made to drive slower, as you want to get there faster. But I don't see how you could argue that driving at 60, rather than 70, would be anything other than safer AND more efficient?
(Note, I didn't say "significantly", but it will no doubt be just a bit safer at 60 than 70, and it will be more efficient. Unless you have a car which is more efficient at 70 than 60, but I think that would be out of the norm.)
Youve got two different going arguments there(Note, I didn't say "significantly", but it will no doubt be just a bit safer at 60 than 70, and it will be more efficient. Unless you have a car which is more efficient at 70 than 60, but I think that would be out of the norm.)
Are you saying you think a 60 limit is safer than a 70 limit or that driving at 60 is safer than driving at 70?
saaby93 said:
aw51 121565 said:
I doubt this particular situation (the proposed M1 scheme) would happen on autoroutes in France, for example, where the population is more spread out and the average population density countrywide is only around 25% that of the UK .
What are the downsides to moving to France? .saaby93 said:
mrmr96 said:
(My bold) Huh? I appreciate you don't agree with being made to drive slower, as you want to get there faster. But I don't see how you could argue that driving at 60, rather than 70, would be anything other than safer AND more efficient?
(Note, I didn't say "significantly", but it will no doubt be just a bit safer at 60 than 70, and it will be more efficient. Unless you have a car which is more efficient at 70 than 60, but I think that would be out of the norm.)
Youve got two different going arguments there(Note, I didn't say "significantly", but it will no doubt be just a bit safer at 60 than 70, and it will be more efficient. Unless you have a car which is more efficient at 70 than 60, but I think that would be out of the norm.)
Are you saying you think a 60 limit is safer than a 70 limit or that driving at 60 is safer than driving at 70?
Who authors these reports?
These statements are retarded:
[b]Increasing the capacity of the motorway has the potential to lead to more
vehicles using the motorway. A maximum mandatory speed limit set at a
level below the national speed limit along the M1 will manage traffic growth[/b]
So, we increase the capacity of the road to help more vehicles use it, but then limit that capacity by putting in place limits to traffic flow to avoid any extra emissions from the greater number of users?
Seriously?
And:
[b]In addition, vehicle emissions will be lower from vehicles operating at a
maximum of 60mph[/b]
Eh? Someone needs there arse kicked for that one^^^. I'd love to see the data behind it. But i guess it hasn't generated by anyone who actually understands vehicle tailpipe emissions vs speed and crucially type. (Hint, compare a modern passenger car tailpipe Nox at 70mpg, and at 60mph, and that of a HGV at just 56mph. Then tell me which you would remove to reduce the overall emitted Nox)
And
[b]The proposed maximum mandatory 60mph speed limit will be reviewed to
determine whether it is still needed as air quality improves[/b]
In the same way that other temporary limits are removed? Ie never! (ps, there will be no difference to air quality after the limit is introduced)
I think PH should ask the Highways Agency for the data that backs up there assertion that a 60mph limit will cut emissions? Might make an interesting article!
These statements are retarded:
[b]Increasing the capacity of the motorway has the potential to lead to more
vehicles using the motorway. A maximum mandatory speed limit set at a
level below the national speed limit along the M1 will manage traffic growth[/b]
So, we increase the capacity of the road to help more vehicles use it, but then limit that capacity by putting in place limits to traffic flow to avoid any extra emissions from the greater number of users?
Seriously?
And:
[b]In addition, vehicle emissions will be lower from vehicles operating at a
maximum of 60mph[/b]
Eh? Someone needs there arse kicked for that one^^^. I'd love to see the data behind it. But i guess it hasn't generated by anyone who actually understands vehicle tailpipe emissions vs speed and crucially type. (Hint, compare a modern passenger car tailpipe Nox at 70mpg, and at 60mph, and that of a HGV at just 56mph. Then tell me which you would remove to reduce the overall emitted Nox)
And
[b]The proposed maximum mandatory 60mph speed limit will be reviewed to
determine whether it is still needed as air quality improves[/b]
In the same way that other temporary limits are removed? Ie never! (ps, there will be no difference to air quality after the limit is introduced)
I think PH should ask the Highways Agency for the data that backs up there assertion that a 60mph limit will cut emissions? Might make an interesting article!
mrmr96 said:
I'm making the assumption that with average speed cameras people will stick to the limits, therefore people will do 60 in a 60 or 70 in a 70. And that driving at 60 is safer than driving at 70.
That's the problem with making assumptions Motorway with inside lanes closed off so they could install average speed cameras, no speed limit no accidents.
Motorway with inside lanes closed off so they could do some work some time, average speed limit, a fatal and a few shunts.
Statistical anomalies perhaps but in which situation do you assume it's safer (when it's not) and which do you take more care?
I wonder if that stretch of M1 has a particularly high volume of HGV traffic?
I also wonder if there is any research out there which examines how much the concertina effect is reduced if the speed limit is lowered from 70 to 60? I believe they have found the variable limits on the M25 very effective for this. I could see how overall emissions might reduce noticeably if you reduce the amount of slowing down and re-accelerating which you sometimes get on busy motorways.
I also wonder if there is any research out there which examines how much the concertina effect is reduced if the speed limit is lowered from 70 to 60? I believe they have found the variable limits on the M25 very effective for this. I could see how overall emissions might reduce noticeably if you reduce the amount of slowing down and re-accelerating which you sometimes get on busy motorways.
Max_Torque said:
I think PH should ask the Highways Agency for the data that backs up there assertion that a 60mph limit will cut emissions? Might make an interesting article!
I think they are probably using a model like this one;http://naei.defra.gov.uk/resources/3_9_326_136265_...
Unless I'm doing something dumb, that particular model appears to show a c. 32% increase in per km NOx from Euro 4/5/6 diesels between 60mph and 70mph.
It also appears to show a 7.5% reduction in NOx from equivalent petrol cars over the same speed increment.
Can they not impose a special speed limit for dag-dags?
Gixer said:
With an ever increasing number of our NSL roads becoming 50,40 or even 30mph, I wondered how long it would be before motorways were ruined as well
I see a future where motorways will be 50, other roads 30 and town roads 20....
Now that is depressing. I see a future where motorways will be 50, other roads 30 and town roads 20....
Surprised the story wasn't relating to the M4 in South Wales where the Newport>Cardiff section has 50mph average speed cameras whilst building work was done but now they have been left in place apparently to reduce the noise.
Gixer said:
With an ever increasing number of our NSL roads becoming 50,40 or even 30mph, I wondered how long it would be before motorways were ruined as well
I see a future where motorways will be 50, other roads 30 and town roads 20....
My thoughts exactly - and I've said as much on PH; your vision is exactly the same as mine.I see a future where motorways will be 50, other roads 30 and town roads 20....
I don't give it til the end of the decade - maybe 2025 at the latest - before the motorway is 50 and NSL is 30 or maybe 40. There is no doubt whatsoever in my mind.
otolith said:
Max_Torque said:
I think PH should ask the Highways Agency for the data that backs up there assertion that a 60mph limit will cut emissions? Might make an interesting article!
I think they are probably using a model like this one;http://naei.defra.gov.uk/resources/3_9_326_136265_...
Unless I'm doing something dumb, that particular model appears to show a c. 32% increase in per km NOx from Euro 4/5/6 diesels between 60mph and 70mph.
It also appears to show a 7.5% reduction in NOx from equivalent petrol cars over the same speed increment.
Can they not impose a special speed limit for dag-dags?
(note, lots of studies note that Nox emissions is increasing as a proportion of total tailpipe emissions on lower emission limit vehicles (diesel & gasoline) but fail to note that the absolute emissions of Nox are reducing, and your lungs care about absolute values not relative ones)
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!
And as a final point, do we have any real data to back up that this increased pollution is actually resulting in health issues to the local population?
Max_Torque said:
Great spread sheet, but without reference source data used to generate the Nox vs speed co-efficients it is meaningless! I've just looked at some of my actual test data for tailpipe emissions. Neither the EU5/6 derv or the EU5 Gasoline show any significant absolute change in tailpipe nox between 60mph and 70mph! (because the aftertreatment at those loads is incredibly efficient, and the actual necessary Pmax change from 60mph to 70mph is very small)
Quite - but these are the kind of assumptions they will be working to. And a large (relative) reduction in a small (absolute) amount adds up when multiplied by huge numbers of vehicles.Max_Torque said:
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!
(...)
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!)
Difference is that a speed limit reduction is easily imposed and a reduction in goods vehicle traffic is not. Restrictions on freight would also be seen as more economically damaging - people's private travelling time seems to be considered entirely worthless where speed limits are concerned.(...)
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!)
Max_Torque said:
And as a final point, do we have any real data to back up that this increased pollution is actually resulting in health issues to the local population?
I don't think they have a choice, they have to meet air quality standards to comply with EU legislation.Gassing Station | General Gassing | Top of Page | What's New | My Stuff