Smart motorways to end 🚗

[wine~o]

when you are opening the hard shoulder the speed limit needs to be reduced to 30mph otherwise it's just too dangerous.

But you said

the worst thing that can happen is for traffic to have to stop, even if only for a few seconds, that quickly grows into a huge jam.

So which is it?

If as you suggest the traffic is slowed to 30, everyone will stop, even if it goes down by 10mph at intervals, 90% of the time folk ignore the overhead signs, because 70% of the time the signs are wrong because the information displayed has not been updated. So those bombing along at 70 will come to an abrupt halt as they realise those infront have slowed down, so it goes on till you stop.

If the speed limit is lowered why will people have to stop? As you say you just need to start the reduction as far back as possible.

The thing is that people (most anyway) don't know how motorways work, even normal motorways. The over head gantries wll have a speed limit posted, they don't go from NSL to 30, they'll go from 60 to 50 to 40 over a few gantries... or the red X... probaly 80/90% ignore those signs. If everyone drove sensibly and concentrated on the road there would be no issue.

For example, my cousin Gary drives a powerful merc. joins motorways from the sliproad and immediatly accelerates to the outside lane @ 110 MPH without making proper observations.

[Someone-Else]

If the speed limit is lowered why will people have to stop? As you say you just need to start the reduction as far back as possible.

They will stop at the start of the speed reduction.

Folk bombing along at 70
speed limit signs come on
Folk slow down
Those behind don't slow down.........until they realise those in front have slowed
The person in front slows quite a lot, so the ones behind slow even more
Those behind don't slow down.........until they realise those in front have slowed
The person in front slows quite a lot, so the ones behind slow even more
Those behind don't slow down.........until they realise those in front have slowed
The person in front slows quite a lot, so the ones behind slow even more
The ones at the end stop.

[Someone-Else]

they'll go from 60 to 50 to 40 over a few gantries

only sometimes. Often seen them do that then last one is 60

[Someone-Else]

joins motorways from the slip road and immediately accelerates to the outside lane @ 110 MPH without making proper observations.

Seen very similar, around 60 and middle lane

[Rorschach]

If the speed limit is lowered why will people have to stop? As you say you just need to start the reduction as far back as possible.

They will stop at the start of the speed reduction.

Folk bombing along at 70
speed limit signs come on
Folk slow down
Those behind don't slow down.........until they realise those in front have slowed
The person in front slows quite a lot, so the ones behind slow even more
Those behind don't slow down.........until they realise those in front have slowed
The person in front slows quite a lot, so the ones behind slow even more
Those behind don't slow down.........until they realise those in front have slowed
The person in front slows quite a lot, so the ones behind slow even more
The ones at the end stop.

That's why you use the gantries to slow the speed gradually over ideally several miles.

[Argyll]

I've no idea what they are.

[Someone-Else]

That's why you use the gantries to slow the speed gradually over ideally several miles

I understand what you mean, I am saying it does not work. No matter where it starts, you will still get

Folk bombing along at 70
speed limit signs come on
Folk slow down
Those behind don't slow down.........until they realise those in front have slowed
The person in front slows quite a lot, so the ones behind slow even more
Those behind don't slow down.........until they realise those in front have slowed
The person in front slows quite a lot, so the ones behind slow even more
Those behind don't slow down.........until they realise those in front have slowed
The person in front slows quite a lot, so the ones behind slow even more
The ones at the end stop.

[big-all]

I've no idea what they are.

a 3 lane plus shoulder turned into a 4 lane running with lay byes every 500m and electronic almost instant notification off obstruction so perhaps 3-5 mins warning but usually less off danger and auto reduce speed warnings this is quite dangerous but statistically not good but nearing acceptable risk
they then diminish the cost by increasing gaps to perhaps 1250-1500m they then introduce before full electronic protection provided and aim for 10 mins before manual notification and action but often takes far longer and electronic then fails to get fitted so massive danger and and many more deaths to save costs

[Argyll]

I've no idea what they are.

a 3 lane plus shoulder turned into a 4 lane running with lay byes every 500m and electronic almost instant notification off obstruction so perhaps 3-5 mins warning but usually less off danger and auto reduce speed warnings this is quite dangerous but statistically not good but nearing acceptable risk
they then diminish the cost by increasing gaps to perhaps 1250-1500m they then introduce before full electronic protection provided and aim for 10 mins before manual notification and action but often takes far longer and electronic then fails to get fitted so massive danger and and many more deaths to save costs

Cheers Al. Must only be down south.

[Rorschach]

That's why you use the gantries to slow the speed gradually over ideally several miles

I understand what you mean, I am saying it does not work. No matter where it starts, you will still get

Folk bombing along at 70
speed limit signs come on
Folk slow down
Those behind don't slow down.........until they realise those in front have slowed
The person in front slows quite a lot, so the ones behind slow even more
Those behind don't slow down.........until they realise those in front have slowed
The person in front slows quite a lot, so the ones behind slow even more
Those behind don't slow down.........until they realise those in front have slowed
The person in front slows quite a lot, so the ones behind slow even more
The ones at the end stop.

Except that clearly doesn't happen.

[Tom d'Angler]

Years ago there was a documentary about motorways and why there are so many traffic jams when there is no obvious accident and, using helicopter footage (it was before drones), it showed traffic merrily moving along at around 70mph and then the knock-on effect of someone just touching their brakes very slightly, often because they are getting a little too close to the car in front. The car behind touched their brakes harder, the car behind even harder, and so on until several hundred yards back the cars end up stopping completely. It went on to explain that this was due to each driver not reacting to brake lights ahead quickly enough and then overreacting to them, creating a snowball effect going backwards through the traffic until it eventually comes to a halt.

The documentary went on to show, using computer simulation, how variable speed limits of 60 and 50 would prevent this happen when traffic starts to build up on a motorway and it was very convincing. It was one of the things that led the government of the day to experiment with variable speed limits and, in turn, that eventually led to smart motorways.

When the first smart motorway was introduced, it quickly became clear that the hard shoulder became a death trap in the event of a car breaking down, even more so when visibility was poor, but the idiots at the DoT were too proud to withdraw the idea, despite the AA, RAC, police and fire service all lobbying for them to be withdrawn with immediate effect and many lives have been needlessly lost as a result of the government's dithering.

[APDIY]

I can remember the days when a substantial number of wide two way roads had a third, middle lane painted in. There weren’t any priority markings as there are now, e.g. two lanes going up a steep hill, one down with a clear double white “banning” overtaking.
This “chicken driver” middle lane was eventually eliminated after the death toll hit record levels from head on collisions.
“Lessons from history . . . . . “?

[Grendel]

A plumber I worked with had just such an accident on a section of the A5 near Nuneaton . Head on crash although luckily he survived but suffered something like 10% brain damage.

[Someone-Else]

Except that clearly doesn't happen.

Are you sure about that?

Years ago there was a documentary about motorways and why there are so many traffic jams when there is no obvious accident and, using helicopter footage (it was before drones), it showed traffic merrily moving along at around 70mph and then the knock-on effect of someone just touching their brakes very slightly, often because they are getting a little too close to the car in front. The car behind touched their brakes harder, the car behind even harder, and so on until several hundred yards back the cars end up stopping completely. It went on to explain that this was due to each driver not reacting to brake lights ahead quickly enough and then overreacting to them, creating a snowball effect going backwards through the traffic until it eventually comes to a halt.

[Rorschach]

Are you sure about that?

Properly managed it doesn't, the speed is decreased slowly over a long distance so there is no sudden stopping which is the cause of phantom traffic jams.

Problem is we don't have enough smart motorway to make this truly effective and people don't follow the signage or the proper procedure. Case in point, I was on the M5 this week, gantries were on to slow the traffic, 60, then 50 and then 40. No one slowed down until they hit the traffic jam.