Cutting speed limits for cleaner air?

[richie99]

fblm said:

Not so fast with your simple physics. According to the US dept of energy midsize petrol saloon's peak MPG is achieved at 55 mph, where it's 5% more efficient than at 45mph...
https://www.afdc.energy.gov/data/10312

I struggle to believe this is correct. The statement, not the fact they said it. I have a run up the M1 on Friday so will have plenty of time to try out cruising at 45mph. Might be a struggle to reach 55 but will give it a try.

[Plymo]

Went through the M4 section through Newport again at 4am this morning - the variable signs were all blank. Perhaps they've decided to only do the 50 limit when it's busy?

[Willy Nilly]

Evanivitch said:

Diesel engines blowing smoke however is very much a case of overfuelling, not quite the nuance of detail I was looking for.

The pre emission controlled diesels would blow a haze out under load.

[wc98]

Rovinghawk said:

wc98 said:

i think he means................

I'm aware, thanks. It was just the awful way he was describing it whilst telling others to study.

parrot accepted.

[Pan Pan Pan]

Just got back from a 1700 mile round trip, which included continental roads,, and the thought of having to do that journey at 50 mph would make the journey a true nightmare, and simply not worth doing, on the basis of time constraints alone. (strange how the motorway speed limit is 80 mph in France?)
following the comments made by some, I decided to do some checking, and found out that where I travelled at 50mph, my fuel consumption Increased. when compared to travelling at 70.
The idea that for cars, aerodynamics is the key feature in achieving best fuel consumption is absolute b*llocks. especially when the way most cars are built today is taken into account.
My car will just about travel at 50 mph in top gear one up. (it will not do that comfortably with passengers and luggage) but it does not like it, and I have the engine laboring, and the shift indicator continually telling me to change down, the moment even a slight uphill section is encountered, and surprise! surprise! the indicated fuel consumption increases by 2.8 gallons compared to travelling at 70 mph in top gear.
At 50mph in fourth gear the rpm is 1950, whilst at 70 mph in Fifth it is 2000 rpm. so for an increase of just 50rpm in fifth gear I travel a further 20 miles with the engine turning over at a speed at which it is comfortable, and producing the best fuel consumption/least pollution .
The fuel consumption at 50 in fourth gear is actually better than when traveling at 50 in fifth gear, because the engine is turning over at nearer to its optimum speed.
As for a 50mph limit making the roads more efficient, that too appears to be absolute b*llocks.
All that happens when a 50mph limit is put up on the overhead gantries, is that the traffic bunches up, and then slows to a crawl, moving at no where near 50 mph. I firmly believe that spuriously applied 50mph limits don't cure traffic jams, they cause them.
By using 50mph limits it means that vehicles will need to be on the roads for longer to complete a given journey, so there will more, not less cars on the road at a given time.
The simple truth is that if certain drivers cannot safely cope with a 70 mph limit they should either avoid roads that have that limit, or stay off the roads entirely, as they are not suited to driving in the conditions that exist on modern roads.

Edited by Pan Pan Pan on Tuesday 3rd July 10:46

[Welshbeef]

Can someone answer

If you have an EV can you go at 70mph due to zero emissions? Or also you have to suffer with the ICE? Or PHeVs could run electric only that section

[Evanivitch]

Welshbeef said:

Can someone answer

If you have an EV can you go at 70mph due to zero emissions? Or also you have to suffer with the ICE? Or PHeVs could run electric only that section

No and no.

The original part of the 50mph section in Port Talbot was brought in for noise reasons.

[oyster]

Pan Pan Pan said:

Just got back from a 1700 mile round trip, which included continental roads,, and the thought of having to do that journey at 50 mph would make the journey a true nightmare, and simply not worth doing, on the basis of time constraints alone. (strange how the motorway speed limit is 80 mph in France?)
following the comments made by some, I decided to do some checking, and found out that where I travelled at 50mph, my fuel consumption Increased. when compared to travelling at 70.
The idea that for cars, aerodynamics is the key feature in achieving best fuel consumption is absolute b*llocks. especially when the way most cars are built today is taken into account.
My car will just about travel at 50 mph in top gear one up. (it will not do that comfortably with passengers and luggage) but it does not like it, and I have the engine laboring, and the shift indicator continually telling me to change down, the moment even a slight uphill section is encountered, and surprise! surprise! the indicated fuel consumption increases by 2.8 gallons compared to travelling at 70 mph in top gear.
At 50mph in fourth gear the rpm is 1950, whilst at 70 mph in Fifth it is 2000 rpm. so for an increase of just 50rpm in fifth gear I travel a further 20 miles with the engine turning over at a speed at which it is comfortable, and producing the best fuel consumption/least pollution .
The fuel consumption at 50 in fourth gear is actually better than when traveling at 50 in fifth gear, because the engine is turning over at nearer to its optimum speed.
As for a 50mph limit making the roads more efficient, that too appears to be absolute b*llocks.
All that happens when a 50mph limit is put up on the overhead gantries, is that the traffic bunches up, and then slows to a crawl, moving at no where near 50 mph. I firmly believe that spuriously applied 50mph limits don't cure traffic jams, they cause them.
By using 50mph limits it means that vehicles will need to be on the roads for longer to complete a given journey, so there will more, not less cars on the road at a given time.
The simple truth is that if certain drivers cannot safely cope with a 70 mph limit they should either avoid roads that have that limit, or stay off the roads entirely, as they are not suited to driving in the conditions that exist on modern roads.

Edited by Pan Pan Pan on Tuesday 3rd July 10:46

Why would the way modern cars are built reduce the aerodynamic effect between 2 different speeds?

It doesn't matter if it's a house brick or a super-modern car - if you increase the speed the same, the aerodynamic load increases the same. Unless you're suggesting modern cars become more aerodynamic with speed (like a DRS system)?

[Timmy45]

Evanivitch said:

Welshbeef said:

Can someone answer

If you have an EV can you go at 70mph due to zero emissions? Or also you have to suffer with the ICE? Or PHeVs could run electric only that section

No and no.

The original part of the 50mph section in Port Talbot was brought in for noise reasons.

Pah, the WAG decide what they want to do then pick some bullst reason to justify it.

[speedking31]

Evanivitch said:

The original part of the 50mph section in Port Talbot was brought in for noise reasons.

Road and wind noise make a significant contribution to overall noise levels, and are still present with an EV.

[Evanivitch]

speedking31 said:

oad and wind noise make a significant contribution to overall noise levels, and are still present with an EV.

Agreed, which is kind of why I mentioned it.

Note, HGV traffic is a big issue on the earlier stretch as the raised motorway section further increases the road noise.

[TheDrBrian]

oyster said:

Pan Pan Pan said:

Just got back from a 1700 mile round trip, which included continental roads,, and the thought of having to do that journey at 50 mph would make the journey a true nightmare, and simply not worth doing, on the basis of time constraints alone. (strange how the motorway speed limit is 80 mph in France?)
following the comments made by some, I decided to do some checking, and found out that where I travelled at 50mph, my fuel consumption Increased. when compared to travelling at 70.
The idea that for cars, aerodynamics is the key feature in achieving best fuel consumption is absolute b*llocks. especially when the way most cars are built today is taken into account.
My car will just about travel at 50 mph in top gear one up. (it will not do that comfortably with passengers and luggage) but it does not like it, and I have the engine laboring, and the shift indicator continually telling me to change down, the moment even a slight uphill section is encountered, and surprise! surprise! the indicated fuel consumption increases by 2.8 gallons compared to travelling at 70 mph in top gear.
At 50mph in fourth gear the rpm is 1950, whilst at 70 mph in Fifth it is 2000 rpm. so for an increase of just 50rpm in fifth gear I travel a further 20 miles with the engine turning over at a speed at which it is comfortable, and producing the best fuel consumption/least pollution .
The fuel consumption at 50 in fourth gear is actually better than when traveling at 50 in fifth gear, because the engine is turning over at nearer to its optimum speed.
As for a 50mph limit making the roads more efficient, that too appears to be absolute b*llocks.
All that happens when a 50mph limit is put up on the overhead gantries, is that the traffic bunches up, and then slows to a crawl, moving at no where near 50 mph. I firmly believe that spuriously applied 50mph limits don't cure traffic jams, they cause them.
By using 50mph limits it means that vehicles will need to be on the roads for longer to complete a given journey, so there will more, not less cars on the road at a given time.
The simple truth is that if certain drivers cannot safely cope with a 70 mph limit they should either avoid roads that have that limit, or stay off the roads entirely, as they are not suited to driving in the conditions that exist on modern roads.

Edited by Pan Pan Pan on Tuesday 3rd July 10:46

Why would the way modern cars are built reduce the aerodynamic effect between 2 different speeds?

It doesn't matter if it's a house brick or a super-modern car - if you increase the speed the same, the aerodynamic load increases the same. Unless you're suggesting modern cars become more aerodynamic with speed (like a DRS system)?

NO NO NO NO. Planes have a best cruise speed, so do cars. There's a speed where the thrust matches weight for the least AOA and this lifts the weight off the wheel bearings reducing drag.

/s

[Pan Pan Pan]

oyster said:

Pan Pan Pan said:

Just got back from a 1700 mile round trip, which included continental roads,, and the thought of having to do that journey at 50 mph would make the journey a true nightmare, and simply not worth doing, on the basis of time constraints alone. (strange how the motorway speed limit is 80 mph in France?)
following the comments made by some, I decided to do some checking, and found out that where I travelled at 50mph, my fuel consumption Increased. when compared to travelling at 70.
The idea that for cars, aerodynamics is the key feature in achieving best fuel consumption is absolute b*llocks. especially when the way most cars are built today is taken into account.
My car will just about travel at 50 mph in top gear one up. (it will not do that comfortably with passengers and luggage) but it does not like it, and I have the engine laboring, and the shift indicator continually telling me to change down, the moment even a slight uphill section is encountered, and surprise! surprise! the indicated fuel consumption increases by 2.8 gallons compared to travelling at 70 mph in top gear.
At 50mph in fourth gear the rpm is 1950, whilst at 70 mph in Fifth it is 2000 rpm. so for an increase of just 50rpm in fifth gear I travel a further 20 miles with the engine turning over at a speed at which it is comfortable, and producing the best fuel consumption/least pollution .
The fuel consumption at 50 in fourth gear is actually better than when traveling at 50 in fifth gear, because the engine is turning over at nearer to its optimum speed.
As for a 50mph limit making the roads more efficient, that too appears to be absolute b*llocks.
All that happens when a 50mph limit is put up on the overhead gantries, is that the traffic bunches up, and then slows to a crawl, moving at no where near 50 mph. I firmly believe that spuriously applied 50mph limits don't cure traffic jams, they cause them.
By using 50mph limits it means that vehicles will need to be on the roads for longer to complete a given journey, so there will more, not less cars on the road at a given time.
The simple truth is that if certain drivers cannot safely cope with a 70 mph limit they should either avoid roads that have that limit, or stay off the roads entirely, as they are not suited to driving in the conditions that exist on modern roads.

Edited by Pan Pan Pan on Tuesday 3rd July 10:46

Why would the way modern cars are built reduce the aerodynamic effect between 2 different speeds?


It doesn't matter if it's a house brick or a super-modern car - if you increase the speed the same, the aerodynamic load increases the same. Unless you're suggesting modern cars become more aerodynamic with speed (like a DRS system)?

No I am not suggesting that. But the wheels and wheel arches, exhaust systems, catalysers, underbody structural members, trims, external mirrors, suspension arms, springs etc, even the way the windows are set into the cars body, can and do produce drag, On most (even modern) cars it is really only the upper body which is designed to be aerodynamic, and then only when this is commensurate with the styling the manufacturer wants to use. Engineers seem to do relatively little if anything at all, to make the wheels and underbody more aerodynamically efficient.
The whole point of using a motor vehicle is to get from one place to another as fast as possible, commensurate with safety and the general driving ability of the motoring public. To artificially reduce speeds from this, for the spurious benefit of cleaner air, is simply going backwards, and I would guess not what most (but obviously not all) people who drive would want to accept, As I posted earlier some will only be happy when we have regressed to the point of having a man with a red flag walking in front of every vehicle. Luddites.

[Evanivitch]

Pan Pan Pan said:

Engineers seem to do relatively little if anything at all, to make the wheels and underbody more aerodynamically efficient.

Wow, that's probably your most ignorant statement so far.

Nearly all cars use flat underbody panels with only the exhaust and suspension components exposed.

You'll also notice a lot of cars use lips and wind deflectors at the leading tyres. Most alloys are usually detrimental to aerodynamics, but genuine efficiency models (Bluemotion, EfficientDynamics, A2, Insight) tend to do a better job.

[Pan Pan Pan]

Evanivitch said:

Pan Pan Pan said:

Engineers seem to do relatively little if anything at all, to make the wheels and underbody more aerodynamically efficient.

Wow, that's probably your most ignorant statement so far.

Nearly all cars use flat underbody panels with only the exhaust and suspension components exposed.

You'll also notice a lot of cars use lips and wind deflectors at the leading tyres. Most alloys are usually detrimental to aerodynamics, but genuine efficiency models (Bluemotion, EfficientDynamics, A2, Insight) tend to do a better job.

Unlike many aircraft, cars cannot retract their wheels out of the airflow, or generally get the drag inducing items under a car, out of the airflow and inside the body shell
(ever seen how aerodynamic the underside of the engine/gearbox, or an exhaust box/catalyzer ,or a spare wheel carrier is?) so aerodynamics in cars will necessarily be a limited least worst case exercise, only a few high end cars have true underbody aerodynamics, and full underbody sheathing, The only aerodynamic suspension I have ever seen on cars is on race cars and some Caterhams. If you can provide photos of ordinary cars with full underbody aerodynamics I would be interested to see what they are, and how many of the total cars on the road they represent
I am always interested to see the underside of many cars, even those up on car transporters on the roads, and if you can describe those as being aerodynamic, you must live on a different planet to everyone else.

[Evanivitch]

Pan Pan Pan said:

If you can provide photos of ordinary cars with full underbody aerodynamics I would be interested to see what they are, and how many of the total cars on the road they represent
I am always interested to see the underside of many cars, even those up on car transporters on the roads, and if you can describe those as being aerodynamic, you must live on a different planet to everyone else.

I never stated cars have full aerodynamic underbodies.

I think we're all aware you have no understanding of time or physics so it's unsurprising you also think you're an expert on aerodynamics too.

[CubanPete]

Previous said:

Well, reducing the limit reduces emissions as fuel efficiency rises... But capacity rises also and as thats taken up surely the extra vehicles will collectively produce more....

(I keep being told by planner types if they build more roads then those roads are then filled...(which ironically is actually the point...))

Suspect its really about capacity improvements ro hide the lack of infrastructure investment - M4 past port talbot has no room for fancy fandango managed / smart mway.

Capacity reduces with speed reductions..

There'll just be a polluting traffic build up elsewhere..

[Kawasicki]

Evanivitch said:

Pan Pan Pan said:

If you can provide photos of ordinary cars with full underbody aerodynamics I would be interested to see what they are, and how many of the total cars on the road they represent
I am always interested to see the underside of many cars, even those up on car transporters on the roads, and if you can describe those as being aerodynamic, you must live on a different planet to everyone else.

I never stated cars have full aerodynamic underbodies.

I think we're all aware you have no understanding of time or physics so it's unsurprising you also think you're an expert on aerodynamics too.

Full underbody aero

[Evanivitch]

Kawasicki said:

Full underbody aero

Kind of what I said previously, flat underbody with the exception of Exhaust and suspension. For those reasons I wouldn't call it full underbody aero.

[Kawasicki]

Evanivitch said:

Kawasicki said:

Full underbody aero

Kind of what I said previously, flat underbody with the exception of Exhaust and suspension. For those reasons I wouldn't call it full underbody aero.

So do you think it was a Friday afternoon and they just said “that’ll do”, or maybe they considered and engineered the entire underbody function, including aerodynamics.