How do we value our time?

[Downsizer]

Comparing 200 miles at 70mph and 50 mpg with 200 miles at 60 mph and 60 mpg saves half an hour of journey time and costs an extra £4 in fuel, valuing our time at £8 per hour, about the minimum wage.  If the government is serious about reducing emissions, a national 60 mph speed limit would make a significant difference.  It would also reduce the frequency and severity of road accidents.  Probably not a vote winner though!

[nowster]

Unlikely to reduce accidents. The national speed limit of 70mph only applies on certain dual carriageways and motorways, and to cars and motorcycles only. Lorries and vans have a lower limit of 60mph, with HGVs limited to 56mph.

It was also tried before during the 1970s oil crisis.

During December 1973, the government reduced the country’s speed limits in response to the oil crisis. All national 70MPH speed limits were ground down to 50 MPH. It wasn’t until May 1974 that this restriction was lifted.

By December 1974, an energy consumption initiative placed another restriction upon national speed limits. Single and dual carriageway roads were slowed down to 50MPH under this initiative.

On June 1977, the government eased off and raised single-carriageway roads to 60MPH and dual carriageways to 70MPH. Finally, we reached the limits we recognise today. In 1978, our 70 MPH national limit was made permanent.

https://www.gocarwarranty.co.uk/news/history-of-the-uk-70mph-speed-limit/334179

It's the inappropriate use of speed that causes accidents. Idiots will continue to be idiots, and many will continue to ignore speed limits.

[ColinS]

One road local to me was at the national speed limit (60) several years back and an average traffic speed of 48mph as measured by the local authority.

In their infinite wisdom, a 50mph limit was imposed and the average traffic speed went up 52mph.  Explain that .

[Downsizer]

Variable speed limits on some motorways reduce bunching and help to achieve a steady flow of traffic, reducing the accident risk.

[culzean]

I think when 'smart motorways' ( LOL) are allowing hard shoulder to be used ( and it should only be used in peak times ) the speed limit should automatically be set at 40mph, a motorway is one of the safest roads in UK,  a smart motorway one of the most dangerous.   

[nowster]

One road local to me was at the national speed limit (60) several years back and an average traffic speed of 48mph as measured by the local authority.

In their infinite wisdom, a 50mph limit was imposed and the average traffic speed went up 52mph.  Explain that .

At NSL it probably felt a bit dangerous to drivers and drove to the conditions, but at 50mph people were probably thinking, "If it's signed at 50mph it must be safe to drive at 50mph or a little more."

The change in speed limit might also have coincided with changing the road markings too.

[nowster]

I think when 'smart motorways' ( LOL) are allowing hard shoulder to be used ( and it should only be used in peak times ) the speed limit should automatically be set at 40mph, a motorway is one of the safest roads in UK,  a smart motorway one of the most dangerous.

I believe that dynamic hard shoulder use will not be used for any current or future schemes, and all lane running is the only option if the motorway is to be converted to a "smart" one.

[Jocko]

The Smart motorways beside me do not have all lanes running and still retain a hard shoulder. At some points, it doubles as a bus lane but then there are large laybys as well.

[Kremmen]

The M25 is known as London's orbital car park as it's often stationary for large parts of the day in certain stretches.

Back in 2004/5 they widened the western section from 3 to 4 lanes. During that time they enforced a 40mph limit between junctions 11 (M3) and J15 (M4).

During those 2 years the traffic just flowed and I saved about 15 to 30 mins day going home at 16:00

[culzean]

Nightmare of 'smart' sections on M6, 'safety bays' over a mile apart ( they have been working on them after complaints, but long sections of M6 are 'up in the air' on stilts, so adding extra bays difficult )  cannot even get behind the barrier as some places the other side of barrier is 60 foot+ drop, or there is a concrete wall there.  Original spec was bays 1/3 to 1/2 mile apart until the bean counters took over.  On parliament channel on TV i was watching the 'smart motorway parliamentary group, https://smartmotorwayskill.co.uk/all-party-parliamentary-group-report/      The MP's were quizzing the civil servants about the safety angle,  they made the civil servants look stupid, they asked them questions like 'have you ever been in a vehicle broken down on a 'normal' motorway hard shoulder ( non of them had ) and then 'can you imagine being broken down in a live lane,  where the roadside emergency services will not come out to you because it is too dangerous for their people'.  The overwhelming case made for smart motorways was cost, safety does not even come into it. 

[richardfrost]

Yesterday, travelling from West Yorkshire to North Yorkshire, and again on the return journey, I had the pleasure of one of Europe's busiest motorways. The M62 Smart Motorway between Jn 25 and Jn 29 (the M1 interchange). Because of prevailing peak conditions and atrocious weather, the variable speed signs were in use. Unbelievably, given they are less than 1/4 mile apart, they were alternating between 40 and 50 at every set. The same happened on the return journey. How the heck is a driver supposed to respond to that?
- Speed up.
- Slow down.
- What about the speed cameras. Are they watching for people going over 40? Over 50? Over 70?
Needless to say, in that short section, there were several minor rear end shunts, all of which added to the need for care as all lane running was going on and off. Adding to the fun is that a couple of junctions have the hard shoulder/fourth lane suddenly becoming the exit lane at least a mile before you reach the exit.

What a recipe for complete disaster. It's only thanks to the pandemic that I no longer need to commute this route into Leeds most days.

[embee]

Yesterday, Friday, I had the misfortune to drive the M5 from Taunton up to Tewkesbury. There were no road works or collisions or breakdowns, but the traffic (more or less full on all 3 lanes all the way) repeatedly ground to a halt and then moved off again. This concertina was simply down to weight of traffic. It wasn't even classic rush hour times.
My average speed was about 30mph for that stretch.
If it had a 40mph mandatory limit, which is the maximum traffic throughflow speed, it would have worked much better, it reduces the concertina effect.

Fortunately I won't have to do that trip again in the forseeable future. Basically just too many vehicles on the roads we have.

[Downsizer]

I remember many years ago learning the maths of queuing theory, which explains this concertina effect.  It also used to be seen in unbraked goods trains as they slowed down.

[nowster]

Yesterday, Friday, I had the misfortune to drive the M5 from Taunton up to Tewkesbury. There were no road works or collisions or breakdowns, but the traffic (more or less full on all 3 lanes all the way) repeatedly ground to a halt and then moved off again. This concertina was simply down to weight of traffic. It wasn't even classic rush hour times.

It's possible to have variable speed limits without all the rest of the Smart Motorway gubbins. The MIDAS system can show up advisory speed limits on the overhead matrix signs when congestion is detected automatically.

Having adjacent alternating speed limits suggests a problem. I have seen (especially in roadworks) where a speed limit is set up on approach, then blank signs for several gantries, eventually resolving in an NSL "all clear". You then get a mixture of reactions from drivers: some who wait for the next sign, and some who assume something's gone wrong and they speed up.

PS. If a variable speed limit changes whilst you're looking at it, enforcement of a reduction doesn't happen until about a minute later.

[ColinS]

PS. If a variable speed limit changes whilst you're looking at it, enforcement of a reduction doesn't happen until about a minute later.

But what happens if you are not looking at it?