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Motorway roadwork speed limits at 60

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 Offwidth 26 Jul 2020

Announced today that the speed limits in roadworks on motorways to be increased to 60 after practical testing of the idea.  This has made sense on safety grounds for years. A particular problem being overcautious drivers driving 50 on their overreading speedometer being constantly overtaken by lorries driving at 50. Then of course the occasional idiot driving 50 on their speedometer staying in the middle lane (blocking lorry overtaking), or worse in the outside lane. This change should increase traffic flow, reduce frustration and keep lorries in the inside lane a lot more.

3
In reply to Offwidth:

Offwidth after the next proposal to remove speedlimits in roadworks all together:

"A particular problem being overcautious drivers driving 60 on their overreading speedometer being constantly overtaken by lorries driving at 60. Then of course the occasional idiot driving 60 on their speedometer staying in the middle lane (blocking lorry overtaking), or worse in the outside lane. This change should increase traffic flow, reduce frustration and keep lorries in the inside lane a lot more."

9
 Tringa 26 Jul 2020
In reply to Offwidth:

I've only read this repost n the BBC News website - https://www.bbc.co.uk/news/uk-england-53541440

and I note it says Highways England it comes after extensive testing and trials, but does it really make a good case for an increase in the speed limit through road works?

The AA said it would, " ... help reduce tailgating by motorists." Tailgating is driving too close the vehicle in front, it has nothing to do with the speed limit. If you are too close to the vehicle in front then reduce your speed.

Highways England found the journey time on a 24 mile was reduced by an average of 68 seconds. Is saving fractionally over one minute a good reason to potentially increasing the risk of injury to road workers?

Dave

2
In reply to Tringa:

I think if you dig a bit deeper what has actually happened is that there is now more flexibility of roadwork speed limits, which makes sense.  There are certainly plenty of examples where 50 seems quite unnecessary.  Similarly we have all been "locked" in to traffic at 50 with a lorry creeping past at 52 about 6" away in a narrow lane.  If the first is now a 60 limit and the second a 40 limit, that makes sense. 

Post edited at 09:05
1
 capoap 26 Jul 2020
In reply to Tringa:

Where are theses road workers you mention?  We sometimes have a game spotting them in particular on the offten over 10 miles of road works/cones on the A55. Sorry I included word works should have been just cones without any indication of works or workers.

2
In reply to MG:

Speaking personally I have spent a LOT of time on the M6 and M4 over the last 20 years, and the introduction of the 50 mph limit was one of the best things to happen, because there was a marked reduction in accidents that was the real source of delays.

I think this is a rubbish idea.

17
In reply to Offwidth:

I noticed this the other day.  It always used to be the case that they would post a limit 10mph below what they expected everyone to actually do, as pre-camera that was what most drivers did, but what then happened is that cameras were introduced without changing the number.

I certainly found it less stressful driving at 60 than 50 because there weren't aggressive lorries wanting to do 56 about 2" off your rear bumper.  Coach limiters are of course set to 62, but there are far fewer coaches than lorries (particularly at the moment) and they tend not to be driven as aggressively.

And yes there are cases where 40 makes sense, though if you need to go to 40 I think you should also think about redesigning the layout so as to avoid it, e.g. go for 2 wider lanes rather than 3 really, really narrow ones.  Or consider using concrete barriers instead of cones.

Post edited at 10:17
 GrahamD 26 Jul 2020
In reply to Offwidth:

I'm happy with the concept of applying 60mph in some cases, but presumably its still case by case ? In some cases 40mph is a lot safer (eg a lot of joining slip roads where cars can match speeds, or sharp transitions across carriageways.).  Incidentally, I'm sure I went through a 60mph roadwork speed limit somewhere on my journey from N.Wales last week.

 lorentz 26 Jul 2020
In reply to Offwidth:

*The Govt:

We've cancelled your summer holiday to Spain... But your trip back from the airport will be fractionally quicker. 

The stick and the carrot.  😁

1
 Franco Cookson 26 Jul 2020
In reply to Offwidth:

Also worth a consideration of the environmental factors. Have you ever done a long (circa 500 mile) trip at 50 MPH? It's crazy how much less fuel you use, particularly in a car with a small engine. I once drove from Sheffield to past Heidelberg on a single tank and the diesel light hadn't even come on. 

I'd love to see the calculation of how much extra fuel will be used by all those extra miles at 65MPH, rather than 55MPH. 

P.s. sorry for clogging up the outside lane by going the speed limit (according to my car). 

14
In reply to Franco Cookson:

IT's a good point.  And a good argument for speed limit of 55mph, which about the speed for maximum fuel efficiency.  (Modern speedometers are pretty accurate too - compare with a GPS to see this.

10
In reply to GrahamD:

The experimental sections are on the M1 around Northamptonshire if I recall.

In reply to MG:

> IT's a good point.  And a good argument for speed limit of 55mph, which about the speed for maximum fuel efficiency.  (Modern speedometers are pretty accurate too - compare with a GPS to see this.

Was.  It's not necessarily the case with modern cars, particularly not those with a 6th gear.  And with an electric, it'll be 1mph.

Post edited at 12:33
2
 Franco Cookson 26 Jul 2020
In reply to Neil Williams:

It definitely varies quite a bit. I think just below 50 is actually most efficient for my 1.6 skoda greenline engine. I've done about 1000 miles on a (about 55L I think) tank when driving in Europe before at about 48MPH (when I was skint), might have had a tail wind... Maybe a big engine with 6 gears might be better at towards 60MPH, but I would be surprised if any ICE car is more efficient above that. Interested to know though, if you know different? What's the craic with like 3L engine cars - I've got no experience of them...  

Edit: also road surface and whether you use cruise control seem to make quite a big difference too. 

Post edited at 12:42
2
 pec 26 Jul 2020
In reply to capoap:

> Where are theses road workers you mention?  We sometimes have a game spotting them in particular on the offten over 10 miles of road works/cones on the A55. Sorry I included word works should have been just cones without any indication of works or workers.


Indeed, there's nothing more frustrating than crawling along at 50mph "for the safety of the workers" on a deserted motorway when the workers are all at home in bed.

I've long argued we just implement the reduced limits when they are actually needed, three deserted lanes on a motorway at midnight does not need a 50 limit when I can drive on a busy single carriageway at 60.

A simple "50mph when the red flag is flying" system or suchlike is all that's needed. Surely that's not beyond the wit of man?

1
In reply to Neil Williams:

It'll vary a bit but it's mostly down to air resistance so won't be far from 55mph for petrol. It's also significantly better at a constant speed, which is more achievable at <70mph.

In reply to pec:

> A simple "50mph when the red flag is flying" system or suchlike is all that's needed. Surely that's not beyond the wit of man?

While some of them are for the installation of smart motorway features, what I don't understand is why they don't use those when there are roadworks on sections where they are installed.  This would allow for exactly what you suggest - 60 in the "coned" area, but 40, 30 or even 20 when people are actually working in a particular location.

OK, they'd be a bit misaligned with the lanes, but it's very rare[1] not to have the same speed on all lanes, and some of the newer systems just show one number on a single larger sign anyway.

[1] I've seen 40-50-60-60 where there was a queue on a slip lane that was in danger of spilling onto the motorway, but it's not common.

Post edited at 13:18
 rj_townsend 26 Jul 2020
In reply to pec:

> A simple "50mph when the red flag is flying" system or suchlike is all that's needed. Surely that's not beyond the wit of man?

The speed limits in the roadworks on the M6 around Coventry (if they're still there) already do this - the louvred signs take care of it.

 Martin Hore 26 Jul 2020
In reply to Offwidth:

> A particular problem being overcautious drivers driving 50 on their overreading speedometer being constantly overtaken by lorries driving at 50. 

Totally agree. The behaviour of some "professional" lorry drivers in these circumstances leaves a lot to be desired. They seem to think that the 50 limit doesn't apply to them and continue to drive at their maximum governed speed. So car drivers have to break the speed limit or suffer being overtaken or tail-gated by HGV's in what are often narrow lanes. Frightening in my experience.

Martin

 Agar Jelly 26 Jul 2020
In reply to Offwidth:

Like "Smart Motorways" and "Herd Immunity" it's the latest example of the gov putting efficiency above decency. It's no great surprise of course and it doesn't mean I have to like it; which is just as well because I don't.

6
 DancingOnRock 26 Jul 2020
In reply to GrahamD:

I’m hoping that essentially it’ll be down to each site to determine what the limit should be rather than applying blanket fixed 50mph. 
 

So maybe lift the restriction at night and lower it to 40mph if the workers are expecting to be on or near the carriageway. 
 

Presumably the issue is if there’s an accident and a car swerves off the motorway at 40mph into a load of workers it’s less likely to kill so many as if it happens at 70mph. 
 

Don’t think it has anything to do with drivers or cars. 

 wercat 26 Jul 2020
In reply to Franco Cookson:

excellent point and it saddens me to think that all the hopes of a silver lining from the lockdown would be less pollution.  I've driven on some long trips trying not to exceed 50 ish through economic necessity and it makes a huge difference dropping from 70.  I also welcome the average speed cameras as you can't drive just to fool the camera any more.

perhaps the payback should be dropping the motorway limit to 60 as we still face the major problem of climate change

Post edited at 17:21
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 wercat 26 Jul 2020
In reply to MG:

I used to think that optimum economy was in the mid 50s till I had to slow down economically.  I also noticed that on long drives into Norfolk when the traffic limits you to long stretches at 40mph the fuel guage seems to stop dropping as you eat the miles so I have a different opinion now.  Not that I'd advocate the misery of a 40mph top speed.  But in the state the climate and environment is in I'd happily see limits dropped on motorways.  Less fuel and less pollution from debris from tyres and brake linings as well as emissions.  Lower maintenance costs as the energy in the vehicle dissipated in braking just to lose velocity falls with the square of the velocity.  that energy translates into polluting debris

Post edited at 17:28
5
In reply to wercat:

Interesting. This has it around 45-50, and seems fairly authoritative.

https://www.rac.co.uk/drive/advice/how-to/fuel-saving-tips/

In reply to DancingOnRock:

> Presumably the issue is if there’s an accident and a car swerves off the motorway at 40mph into a load of workers it’s less likely to kill so many as if it happens at 70mph. 

Concrete barriers (shaped to direct an errant car back onto the road) rather than cones are a far better way to deal with this, and are increasingly used.

In reply to wercat:

I could see a solid argument for basically taking 10mph off all the car NSLs (but not changing the ones for large vehicles), but I doubt it'll happen; electric vehicles will change the argument sooner than it has any chance of doing.

Post edited at 18:01
3
In reply to MG:

I have played around a lot with speed vs fuel in a variety of different vans, cars and motorcycles.

I can't remember the car numbers because I don't spend much time in them. 

My test for this is the A1 between Leeds and scotch corner (I travel that way a lot for work), set the cruise control and once up to speed re set the mpg counter. 

My van, currently a 19 plate Citroen relay. I can average 40 mpg if I keep it at 50, 34 mpg at 60, 30 at 70 and though I didn't spend long enough at 80 to get a true average it was low 20s.

My bike, until Friday it was a 17 plate 1200cc BMW adventure bike. 63 mpg at 50, 55 mpg at 60, 49 at 70, 46 at 80, I tested at 90 but not for long and it dropped to the high 30s but it was only over a few miles like the 80 mph test in my van. 

I'm my opinion 60 mph is the best compromise between speed and efficiency. 

Interesting one on Saturday. I bought a new bike and the Mrs drive the van home. I followed her until we hit the motorway because she had the sat nav then I opened the bike up. I did 80 to 90 all the way home except 1 section roughly a mile long where the traffic was only doing 30 and rubber necking at the accident on the other side. I filtered through at about 50. The Mrs obviously couldn't filter in the van so she has to slow right down and for the rest of the trip she sat at 60 mph. 

The whole trip was 34 miles. I didn't time it but I got home, took my helmet off, put the bike in the garage and was just locking the garage door as she pulled up in the van. Maybe 4 or 5 minutes including the delay at the accident. 

1
 DancingOnRock 26 Jul 2020
In reply to Neil Williams:

As I say. It’ll be down to individual roadworks to decide. If you have a mobile works cutting grass, there’s no need to put concrete barriers down.

 DancingOnRock 26 Jul 2020
In reply to Dax H:

Your definition of ‘filtering’ is not the highway code’s definition. 

8
In reply to DancingOnRock:

Yes, true.  Equally that will tend to be a very short section where you're actually doing it, and could be dynamically displayed via the Smart Motorways displays.  Indeed, if it's only on one side doing 40-50-60-60 might be viable where the displays support it.

In reply to DancingOnRock:

I'd say filtering on a motorcycle at a 20mph speed differential is a bit dangerous, really.  I've no issue with motorcycles filtering, but the speed differential needs to be quite low.

 deepsoup 26 Jul 2020
In reply to MG:

> Offwidth after the next proposal to remove speedlimits in roadworks all together:

> "A particular problem being overcautious drivers driving 60 on their overreading speedometer being constantly overtaken by lorries driving at 60.

The overwhelming majority of the lorries on UK roads are not capable of 60mph - they're legally required to be fitted with speed limiters set to 56mph (90kph) or less.

Post edited at 19:53
In reply to deepsoup:

Downhill no problems!

In reply to deepsoup:

Coaches are limited to 100km/h (62mph) but I find they are generally much less aggressively driven than lorries and far fewer in number too.

 DancingOnRock 26 Jul 2020
In reply to Neil Williams:

Stationary or slow moving traffic. It’s not the differential. 

2
 Toccata 27 Jul 2020
In reply to Dax H:

Amazing what difference speed makes isn't it?

On a 140 mile daily commute (round trip; 4 days a week) ~ 70 % is on motorway or duel carriageway.

If I drive carefully on the B roads and stick to 80 on the faster roads the weekly diesel bill is £54ish (52mpg)

Moving a bit faster on the B roads and edging to 85mph I pay £60.

Battering it on both roads it's closer to £70.

£16 a week to save just over 10 minutes a day seems quite steep.

1
 Offwidth 27 Jul 2020
In reply to Toccata:

I agree about fuel saving but it's at best a red herring in this change and in my view the change will likely save fuel. The fuel use and polution on a motorway with fluctuating speed up to a speed limit of 50 will likely be more than the situation with the evidenced better and safer flow in a 60 speed limit (mainly as lorries need to overtake less so create less congestion). The lower risk in my view is enough on its own to justify the change. Modern cars are pretty fuel efficient at 60 and on a long journey your drive further between breaks (which, given the data, can mean 60 will be more fuel efficient overall).

60 is the new proposed standard limit, other lower speeds apply subject to conditions and circumstances.

On MG's point, lorries are not commonly tailgating on smart motorways with a 60 speed limit, why would they be commonly be doing so on a motorway roadwork restriction of that speed? Tech is already good enough that many employers take action on fuel use, speed, and driving style, for their commercial drivers; getting caught speeding or dangerous driving by the police risks their livelihood.

Post edited at 08:30
1
 twoshoes 27 Jul 2020

In reply to:

Not really relevant to motorway speed limits but something to think about maybe. 

My job sometimes involves me working alongside/in roads - not motorways luckily. I've got high-vis on, cones out, road signs out and it's freaking terrifying. A significant amount of traffic neither slows down or attempts to move out past road works. Some actively drop gears and accelerate past. I've had traffic cones destroyed and men-at-work signs knocked over. Big vehicles squeeze through at speed despite clearly being able to see me. 

Perhaps not directly relevant to this thread and I know that roadworks are often (usually!) deserted but I know I generally think about the people rather than my journey time when I'm passing workers.

 Ian W 27 Jul 2020
In reply to Franco Cookson:

> It definitely varies quite a bit. I think just below 50 is actually most efficient for my 1.6 skoda greenline engine. I've done about 1000 miles on a (about 55L I think) tank when driving in Europe before at about 48MPH (when I was skint), might have had a tail wind... Maybe a big engine with 6 gears might be better at towards 60MPH, but I would be surprised if any ICE car is more efficient above that. Interested to know though, if you know different? What's the craic with like 3L engine cars - I've got no experience of them...  

> Edit: also road surface and whether you use cruise control seem to make quite a big difference too. 


My 3L diesel car won't pull 55 in top (7th, auto box) without some messing with the flappy paddles, and isn't really any more economic at 55 than 65  or 70. On steady long cruises it'll still do 47 - 50mpg at 75 to 80 with cruise control on. Above that the mpg drops somewhat.

I'm hugely impressed with the fuel economy of this car, as it's better on fuel than much much smaller cars I've had in the past, although if I was chasing mpg, I wouldn't have bought a 1.8 tonne 280bhp merc....

 jkarran 27 Jul 2020
In reply to Franco Cookson:

> I'd love to see the calculation of how much extra fuel will be used by all those extra miles at 65MPH, rather than 55MPH. 

Well maintained vehicle drag at cruise speed is dominated by aerodynamic drag which is a function of velocity squared, V^2. Work done is basically fuel burned and is force x distance so a function of V^2. That does assume you can operate the engine at the same efficiency at 55 and 65 but that's a reasonable assumption.

65^2 / 55^2 = 1.39, 39% more fuel burned.

jk

Post edited at 12:11
1
In reply to Ian W:

My 2.2L diesel Mazda 6 does 62-68 mpg for journeys with lots of uninterrupted cruise control at 65 mph and below.  Economy only seems to suffer when cruising above 70 mph - down to around 55mpg.  It's been a recent discovery for me that using cruise control as much as possible adds around 5-10 mpg in economy (presumably as ECUs are better than me at precisely measuring the fuel required to maintain speed).

 Offwidth 27 Jul 2020
In reply to jkarran:

It's clearly not that simple or the fuel use per mile would increase steadily from low speeds when in fact it doesn't for petrol and diesel motors. Most modern car fuel efficiency data between 55 and 65 contradicts that calculation.... actual decreases are much smaller. 8% typically from this site and varying by car.

https://www.mpgforspeed.com/

Post edited at 12:47
 SDM 27 Jul 2020
In reply to Neil Williams:

> The experimental sections are on the M1 around Northamptonshire if I recall.

​​​​Correct. I travel these sections a lot more regularly than I would like. My anecdotal experience:

​​​​- Tailgating and slow speed lane hoggers have both been significantly reduced. I think the biggest factor here is that there is now a greater speed differential between the slowest vehicles and the average HGV speed.

- Congestion caused by concertinaing when entering the roadworks during busy periods also appears to be reduced unsurprisingly.

I still haven't seen a single worker if you exclude the late night workers (for whom there are additional lane closures anyway).

Overall, I think it is a big improvement as long as they are sensible at choosing the sections that need to be 40 or 50. Using the smart motorway infrastructure to adjust the limits as needed would be far better.

In reply to Offwidth:

> Announced today that the speed limits in roadworks on motorways to be increased to 60 after practical testing of the idea.  This has made sense on safety grounds for years. A particular problem being overcautious drivers driving 50 on their overreading speedometer being constantly overtaken by lorries driving at 50. Then of course the occasional idiot driving 50 on their speedometer staying in the middle lane (blocking lorry overtaking), or worse in the outside lane. This change should increase traffic flow, reduce frustration and keep lorries in the inside lane a lot more.

The 'idiots' are the lorry drivers actually going at 56mph, tailgating cars doing about the same. 

So what if some cautious driver is going 5mph slower than you would wish them too? Just chill out till you're out of the roadworks. Have you seen the aftermath of a serious RTA? It's horrible, I don't know how paramedics routinely deal with it.

 Offwidth 27 Jul 2020
In reply to Mike Stretford:

I'd agree they are idiots as well. Strictly speaking the police should be tackling both groups but they are over-stretched. Since the increase to 60 seems to resolve the issue and improve safety and traffic flow it's a win all round without wasting police time.

 Timmd 27 Jul 2020
In reply to Mike Stretford:

> The 'idiots' are the lorry drivers actually going at 56mph, tailgating cars doing about the same. 

> So what if some cautious driver is going 5mph slower than you would wish them too? Just chill out till you're out of the roadworks. Have you seen the aftermath of a serious RTA? It's horrible, I don't know how paramedics routinely deal with it.

I think there can be some dissonance (almost) when driving, where people can lose sight of the consequences of something going awry, of being a 'whoops' away from something grim.

Post edited at 14:56
In reply to Offwidth:

I find my most efficient speed is the one done when following a large vehicle which is punching a nice big hole in the air for me to sit in. White van man is my motorway friend!

One observation as an irregular motorway driver (no motorways here, let alone dual carriageways) is that average speeds seem to have dropped since the late 90's - at that time the fast lane was doing 90 all the time and the slow lane 70 unless there was a lorry/caravan/old mini in it.  Now everything seems to have dropped 10mph.

Post edited at 15:01
In reply to Offwidth:

> I'd agree they are idiots as well. Strictly speaking the police should be tackling both groups but they are over-stretched. Since the increase to 60 seems to resolve the issue and improve safety and traffic flow it's a win all round without wasting police time.

Sure I agree. But there'll always be times when we need 50 limits so I wish they'd tell the truckers to behave too. I really wouldn't want 40 tonnes crashing into me after a tyre blow out or similar!

 Offwidth 27 Jul 2020
In reply to Mike Stretford:

Maybe the police will be better able to deal with dangerous driving in the roadworks that do need 50 and 40 zones now.

In reply to thebigfriendlymoose:

> It's been a recent discovery for me that using cruise control as much as possible adds around 5-10 mpg in economy (presumably as ECUs are better than me at precisely measuring the fuel required to maintain speed).

I find you can get a better mpg by not using cruise control. By backing off a bit going up hill and speeding up a bit going down hill I see better efficiency in my van than I do with the CC on. 

In reply to DancingOnRock:

> Your definition of ‘filtering’ is not the highway code’s definition. 

Maybe not but in 2 or 3 lanes doing 30 with no turnoffs possible I'm happy to progress at 50 mph. The main risk is lane hoppers but you can mitigate this by slowing down and taking extra care if there is room for a car to switch lanes. 

1
 DancingOnRock 27 Jul 2020
In reply to Dax H:

That’s fair enough but you’re breaking the law and won’t get a full insurance pay out if you come a cropper. 

Post edited at 19:09
1
 climbingbadger 27 Jul 2020
In reply to deepsoup:

And yet they still manage to overtake my 58mph Tesco van…

 Ian W 27 Jul 2020
In reply to thebigfriendlymoose:

> My 2.2L diesel Mazda 6 does 62-68 mpg for journeys with lots of uninterrupted cruise control at 65 mph and below.  Economy only seems to suffer when cruising above 70 mph - down to around 55mpg.  It's been a recent discovery for me that using cruise control as much as possible adds around 5-10 mpg in economy (presumably as ECUs are better than me at precisely measuring the fuel required to maintain speed).


Interesting one about beating cruise control - the merc can beat me, as it works with road conditions and the gearbox to maintain the chosen speed, the last car (and current tow car, well loved honda accord diesel) will do anything to exactly maintain the chosen speed, in whatever gear you are in, so I can easily beat it's mpg on cruise. The sad games you play on long journeys.........

In reply to Toerag:

Speed, as an available commodity on the roads in the UK, has been decreasing probably since the mid-late 80's. More traffic, more restrictions, etc.

I'm sure Clarkson has had a decent moan about it somewhere.

In reply to Mike Stretford:

> So what if some cautious driver is going 5mph slower than you would wish them too? Just chill out till you're out of the roadworks. Have you seen the aftermath of a serious RTA? It's horrible  

Seconded. A few years ago I had the misfortune to chance upon an accident where a driver was trapped in a burning vehicle. Despite the frantic efforts of myself and other passing motorists we could neither free him nor extinguish the fire. Horrible doesn't do it justice. Take it from me, it radically changes any casual attitudes you may have in relation to road safety.

In reply to DancingOnRock:

> That’s fair enough but you’re breaking the law and won’t get a full insurance pay out if you come a cropper. 

If I worried about such things I wouldn't be riding a bike in the first place. 

1
 Dave B 28 Jul 2020
In reply to MG:

Yes, the link from the RAC says it well, all this 'the engine is at its most efficient' at... Is not really the point. You want the highest gear with the lowest amount of fuel going into the engine. If you are pushing on your accelerator you are putting more fuel into the engine. Unless your engine management unit is doing odd things... 

 Offwidth 28 Jul 2020
In reply to Dave B:

I agree with that for constant speed driving but can you explain why you think it applies to typical UK congested motorway driving in 50mph roadworks with fluctuating speed (especially given the common concertinaring)? I thought being in too high a gear can increase fuel use in such situations and with the lack of torque response might even be a safety consideration in some situations. There is no way I will ever be in 6th in a 50 limit in such a congested situation with varying speed of flow. Under standard motorway 70 limits at busy times with concertinaring I often stick in the inside lane at 60 for a more relaxing and fuel efficient drive.

Post edited at 08:32
1
 deepsoup 28 Jul 2020
In reply to climbingbadger:

> And yet they still manage to overtake my 58mph Tesco van…

Downhill?  They can defeat their speed limiters easily enough by knocking it into neutral and coasting, illegal but not much chance of being caught.  Tampering with the speed limiter is possible too I guess, also illegal and potentially pretty stiff penalties for that.

Dunno.  I'd have thought digital tachos would have made that sort of malarky more difficult to get away with but I haven't driven a lorry since before they were a thing.  I've been driving a 3.5t supermarket van just lately too.  Mine's limited to 55mph, though the speedo over-reads a bit just like a car, and I've yet to be given a route that goes anywhere near the motorway.   
(That was part of the appeal - the delivery rounds often escape suburban Sheffield and trundle sedately out into the Peak, it was a bit of a treat during 'lockdown' in all the sunshine while there was no traffic apart from all the bicycles and we were temporarily being nice to each other.)

 wintertree 28 Jul 2020
In reply to Offwidth:

An anti-tailgating system of static cameras backed by escalating fines then points would soon sort out the problem this is intended to address, as well as a lot of other dangerous driving.

I’ve no problem with the limit being selectively raised to 60 mph.  
 

 Offwidth 28 Jul 2020
In reply to wintertree:

That would be really good and would seem technologically feasible. 

Easy to log and target persistent offenders to stop it gaining revenue earning rather than safety reputation of some urban dual carriageways and two lane each way roads with 30 limits and average speed cameras (like the 610 into Nottingham from Junction 26, where the 30 speed limit sign for a two lane road is very missable and the first camera conveniently partially hidden in a tree).

In reply to Offwidth:

I worked with an engineer who's opo was run down by a lorry on a motorway project, his body ended up in the live lane. His head was smeared along the road by passing traffic and was about 4' long apparently.

The decision needs to be on the basis of a proper assessment of the risk to contractor staff.

 Offwidth 28 Jul 2020
In reply to blurty:

Which as far as I can tell it has been. My dad was a foreman on the construction and repair of various motorways so I don't need a lesson on the risks to those working on there.

In reply to Offwidth:

Respect to your father

I would be completely unsurprised to hear that Contractors have been told to assume 60mph and put in measures/ controls accordingly. The cart will be ahead of the horse I suspect. Will check.

 jkarran 28 Jul 2020
In reply to Offwidth:

> It's clearly not that simple or the fuel use per mile would increase steadily from low speeds when in fact it doesn't for petrol and diesel motors. Most modern car fuel efficiency data between 55 and 65 contradicts that calculation.... actual decreases are much smaller. 8% typically from this site and varying by car.

The assumption was stated, real engine efficiency isn't constant with speed or load but nor is it radically different across the normal speed and load range given modern cars have lots of gears and ecu feedback so it can be pretty well optimised. Most car engines are, contrary to the assertion in that article designed to operate efficiently across a significant range of speeds and loads which is essential really since that's how cars are used, the compromise made for that tractability is lower peak efficiency. Higher peak efficiency thermodynamic cycles are employed in some hybrids where load and speed are better controlled (and some ICE only vehicles for cruise optimisation, see Koenisegg's freevalve system), usually through variable valve timing. I don't have my sound working but I suspect this short clip from Toyota explains it well  https://www.youtube.com/watch?v=WKKILW3Zj_Y&

I'm pretty sceptical of that 8% figure, it's not even a first order increase with speed. There's something odd going on with those numbers. Rolling resistance of modern heavy cars isn't negligible and it becomes more dominant at lower speeds and there are near constant pumping losses in the engine and there's all the ancillary junk but none of that really explains those figures.

jk

Post edited at 12:28
 Offwidth 28 Jul 2020
In reply to jkarran:

Produce a reference with different figures then...from memory they roughly match the numbers I saw from colleagues working with traffic flow modelling. Real driving on motorways involving lots of forced speed changes are worse than efficiency measurements taken on a constant fixed speed.

Post edited at 12:39
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 jkarran 28 Jul 2020
In reply to Offwidth:

> Produce a reference with different figures then...from memory they roughly match the numbers I saw from colleagues working with traffic flow modelling.

When the theory and the test data are so far apart one has to wonder what methodological quirk might be the cause.

If we're now changing the problem from 'fuel burn at a speed' to 'fuel burn for a journey at an average speed' then obviously the stop start journeys with slower averages will be worse than mid-speed cruising, modern cars are very heavy with quite refined aerodynamics.

> Real driving on motorways involving lots of forced speed changes are worse than efficiency measurements taken on a constant fixed speed.

I'm not debating that.

jk

 Offwidth 28 Jul 2020
 SDM 28 Jul 2020
In reply to Dax H:

> I find you can get a better mpg by not using cruise control. By backing off a bit going up hill and speeding up a bit going down hill I see better efficiency in my van than I do with the CC on. 

I use a combination of the two on quiet motorway journeys: use cruise control but use the buttons to increase/decrease speed to adjust for hills and other drivers.

In my Ford, this can get me very close to the fuel economy of not using cruise control (i.e. within 1mpg over the long term) while being far more comfortable on my legs and less tiring.

It depends on the vehicle though, I've driven Vauxhalls, Hyundais, Skodas and Seats where this isn't very effective because the controls aren't responsive enough or the lag is too great. I've also driven Kias and Citroens where it does work well.

 Dom Connaway 29 Jul 2020
In reply to MG:

> Offwidth after the next proposal to remove speedlimits in roadworks all together:

> "A particular problem being overcautious drivers driving 60 on their overreading speedometer being constantly overtaken by lorries driving at 60.

Lorries are speed-limited to 56mph.

 Dom Connaway 29 Jul 2020
In reply to Dax H:

> If I worried about such things I wouldn't be riding a bike in the first place. 

Breaking the law doesn't worry you? 

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 DancingOnRock 29 Jul 2020
In reply to Dom Connaway:

No having any money to pay for his care when he’s disabled doesn’t worry him. 

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