How do smart motorways operate??

[Chris5156]

If its a real issue then set the lane 4 drop a lot further back, at say 1km away from the junction, then have a left lane start straight after this, that then exits the motorway at the slip road. So the lane 4 disappears at close to the 1/2 mile sign and the new left slip lane starts just after. If thats still too soon take it to the first sign. Also this lane shouldnt have regular lane markings but instead the dashed lines that you see at the slip roads from the start. That way people just see the lane as an extended slip road.

It is a real issue, yes, and I don't think anything you just said would stop it being an issue. You're now proposing narrowing the whole road to three lanes before the exit even begins. It's so absurd I'm starting to wonder how on earth you can even be serious.

Fundamentally, if a significant proportion of traffic leaves a motorway at a single sliproad, there is a reason that countries all around the world use a lane drop. If there was another way of doing it you'd see some places using another method. The fact that there is a consensus across virtually the whole world on this suggests that lane drops are a good, workable way to deal with this situation. So I can't see for the life of me why you think they need replacing with any of this, especially when you say you'd still allow them at motorway to motorway junctions. That's inconsistent and silly. It makes no difference where the sliproad goes. If there's nothing wrong with a lane drop at a motorway to motorway junction where large volumes of traffic leave, then you have to accept there's no sound reason to argue with a lane drop anywhere else in the same circumstances.

So many of your posts go off on a tangent detailing what you think should be done instead of what exists now. I think your ideas would be listened to and appreciated much more if you set out to understand why things are done the way they are and what the benefits of the current approach might be before you set out to radically change things.

[A9NWIL]

If its a real issue then set the lane 4 drop a lot further back, at say 1km away from the junction, then have a left lane start straight after this, that then exits the motorway at the slip road. So the lane 4 disappears at close to the 1/2 mile sign and the new left slip lane starts just after. If thats still too soon take it to the first sign. Also this lane shouldnt have regular lane markings but instead the dashed lines that you see at the slip roads from the start. That way people just see the lane as an extended slip road.

It is a real issue, yes, and I don't think anything you just said would stop it being an issue. You're now proposing narrowing the whole road to three lanes before the exit even begins. It's so absurd I'm starting to wonder how on earth you can even be serious.

Fundamentally, if a significant proportion of traffic leaves a motorway at a single sliproad, there is a reason that countries all around the world use a lane drop. If there was another way of doing it you'd see some places using another method. The fact that there is a consensus across virtually the whole world on this suggests that lane drops are a good, workable way to deal with this situation. So I can't see for the life of me why you think they need replacing with any of this, especially when you say you'd still allow them at motorway to motorway junctions. That's inconsistent and silly. It makes no difference where the sliproad goes. If there's nothing wrong with a lane drop at a motorway to motorway junction where large volumes of traffic leave, then you have to accept there's no sound reason to argue with a lane drop anywhere else in the same circumstances.

So many of your posts go off on a tangent detailing what you think should be done instead of what exists now. I think your ideas would be listened to and appreciated much more if you set out to understand why things are done the way they are and what the benefits of the current approach might be before you set out to radically change things.

OK so I suppose if there isnt space for a 5th lane then maybe a lane drop is the only option. Lane drops when there is a lane gain straight after dont really make a lot of sense to me, but I can understand the queuing traffic at a junction does need somewhere to go.
The reason I understand there merit at a motorway merge diverge is that its usually a fork where the new motorway splits from the current one so the traffic splits between the two quite nicely and no new traffic joins the existing one after. Of course I suppose it would look more like a regular junction if the new motorway didnt fork but rather freeflowed both ways onto the existing motorway.

[WHBM]

Lane drops through junctions are normally an excuse on an ALR or widening project to avoid rebuilding costs of the bridges over the junction, which is then back-applied to the exiting volumes to offer some sort of arithmetical justification. No consideration is given to the weaving thereby introduced. In contrast, where there are requests for additional junctions, weaving issues and associated increased accident liability is the first reason trotted out for not doing it.

The very substantial rebuilding currently under way at M4 J5 Slough East, where there is already a lane drop and no hard shoulder across the junction, shows the expense one is otherwise put to, to maintain through running lanes.

[A9NWIL]

Lane drops through junctions are normally an excuse on an ALR or widening project to avoid rebuilding costs of the bridges over the junction, which is then back-applied to the exiting volumes to offer some sort of arithmetical justification. No consideration is given to the weaving thereby introduced. In contrast, where there are requests for additional junctions, weaving issues and associated increased accident liability is the first reason trotted out for not doing it.

Well there it is, if the situation is its an excuse not to sort the bridges out and nothing to do with queuing traffic then lane drops are an unnecessary problem that causes more trouble than if they didnt have them!

The very substantial rebuilding currently under way at M4 J5 Slough East, where there is already a lane drop and no hard shoulder across the junction, shows the expense one is otherwise put to, to maintain through running lanes.

I guess no one said doing things properly would be cheap, but Im glad that at least some places they are doing the job properly!
I assume they will make M4 J5 wesrtbound 5 lanes wide for a short while before the junction, which will mean widening the bridge over the railway line presumably?

[Jeni]

Lane drops through junctions are normally an excuse on an ALR or widening project to avoid rebuilding costs of the bridges over the junction, which is then back-applied to the exiting volumes to offer some sort of arithmetical justification. No consideration is given to the weaving thereby introduced. In contrast, where there are requests for additional junctions, weaving issues and associated increased accident liability is the first reason trotted out for not doing it.

The very substantial rebuilding currently under way at M4 J5 Slough East, where there is already a lane drop and no hard shoulder across the junction, shows the expense one is otherwise put to, to maintain through running lanes.

Alternatively in the real world where we don't have an axe to grind, much consideration is given to such issues, especially since most Smart Motorways these days continue with 4 lanes through junctions.

[RichardA35]

Lane drops through junctions are normally an excuse on an ALR or widening project to avoid rebuilding costs of the bridges over the junction, which is then back-applied to the exiting volumes to offer some sort of arithmetical justification. No consideration is given to the weaving thereby introduced. In contrast, where there are requests for additional junctions, weaving issues and associated increased accident liability is the first reason trotted out for not doing it.

The very substantial rebuilding currently under way at M4 J5 Slough East, where there is already a lane drop and no hard shoulder across the junction, shows the expense one is otherwise put to, to maintain through running lanes.

..and you are able to give particular examples of the highway engineering community conspiring to falsify figures?

On schemes I have been involved with the traffic figures are the driver to the geometrical provision not the other way round, subject of course to a value for money test; i.e. you test a range of peak flows and provide the lanes forecast to be needed on a suitable percentile peak demand, which will not necessarily include the seasonal holiday peaks or extraordinary events such as pop concerts but most smart motorway schemes will have a fairly low seasonal variation as they are not in the south west.

[wrinkly]

I once read an article by one of the designers of the A75 Annan bypass in which he more or less admitted that they tried as hard as they could to fiddle the traffic figures to make it come out to a dual carriageway, but failed.

[mikehindsonevans]

Returning to an earlier concerns - with recent experience from earlier this week.
Wednesday 20th September, about 1800 hrs; M42 northbound heading up from the M40 having joined at J3A, en-route to the M6Toll to Cheshire. DHSR active, approaching the point where "congestion: use hard shoulder" changes to "use hard shoulder for J4".

I accept that there may not be anyone watching all the cameras (as has been debated to death up-thread and elsewhere). I know that (as this was the first "dynamic hard-shoulder" project delivered by the then-HA in 2007-08) the road re-builders had absolutely carpet-bombed this motorway with cameras and (I thought) sensors. I know that all the matrix signs over the motorway showed "40" across all four lanes - including the hard shoulder.

So how come no-one spotted the huge silver tanker lorry, on the hard shoulder, just behind a black BMW with both drivers out on the hard-shoulder to exchange details (a live running lane, ostensibly at 40mph on all the matrix signs) in the control room? Who left the lane open with clearly-visible obstacles in the hard shoulder?

As my wife observed - "good job we weren't following the instruction to use the hard shoulder".

Mike

[WHBM]

..and you are able to give particular examples of the highway engineering community conspiring to falsify figures?

Sure. In fact, thinking about this thread, I noticed a good example as I drove both ways round the northern M25 today. The A41 junction, J20, near Watford, always has notably little traffic leaving the motorway. In fact, it's one of those junctions where if the M25 is jammed it's worthwhile to take the exit and go down to the roundabout and back up again, often not stopping at all while doing so. Yet when the Smart 4-laning was done it was given lane drops, just like the next junction along with the M1. Unfortunately, unlike the M1 junction, at the A41 junction they are completely unjustified by the flows.

I can also remember, way back in University times in the 1970s, the widening of the M20 Maidstone bypass from 2 lanes (yes, that's how it once was, where it's now a quad carriageway) to 3 lanes. There was a lane dropped junction which was left at 2 lanes, the consulting engineers justified this by it being "where 20% of traffic leaves the motorway". Now anyone with basic arithmetic would appreciate the inconsistency here, which we did. The lecturer was going to point this out, but we beat him to it.

[betweenmways]

Somewhat related to the original post, though moreso the question in the post title...

Last night, joining the M4 from the M32, speed limit was set to 50 on the slip, then the next gantry on the main carriageway was 40. Notably, the hard shoulder was in use. However, 200 yards further on was a broken down vehicle on the hard shoulder with two service vehicles behind (at least one was police) with their lights on.

I really don't understand why the hard shoulder was not closed - it scares me to be honest. While I don't know the specific circumstances, that unless it was the end of a police chase, the vehicle must have been there long enough for the hard shoulder to have been closed. Surely?

[A9NWIL]

Somewhat related to the original post, though moreso the question in the post title...

Last night, joining the M4 from the M32, speed limit was set to 50 on the slip, then the next gantry on the main carriageway was 40. Notably, the hard shoulder was in use. However, 200 yards further on was a broken down vehicle on the hard shoulder with two service vehicles behind (at least one was police) with their lights on.

I really don't understand why the hard shoulder was not closed - it scares me to be honest. While I don't know the specific circumstances, that unless it was the end of a police chase, the vehicle must have been there long enough for the hard shoulder to have been closed. Surely?

It sounds like what is needed is for sensors in the actual tarmac to sense stationary vehicles, which can then set of a signal in the control centre so that staff can check and get lanes closed as needed.
It cant be automatic as there could be heavy traffic thats stop/start.

[RichardA35]

Somewhat related to the original post, though moreso the question in the post title...

Last night, joining the M4 from the M32, speed limit was set to 50 on the slip, then the next gantry on the main carriageway was 40. Notably, the hard shoulder was in use. However, 200 yards further on was a broken down vehicle on the hard shoulder with two service vehicles behind (at least one was police) with their lights on.

I really don't understand why the hard shoulder was not closed - it scares me to be honest. While I don't know the specific circumstances, that unless it was the end of a police chase, the vehicle must have been there long enough for the hard shoulder to have been closed. Surely?

It sounds like what is needed is for sensors in the actual tarmac to sense stationary vehicles, which can then set of a signal in the control centre so that staff can check and get lanes closed as needed.
It cant be automatic as there could be heavy traffic thats stop/start.

Sounds like someone needs to invent a system of motorway incident detection and automatic signal activation. I can't believe it hasn't been done before now.

[WHBM]

Given that "Smart" motorways have 100% CCTV, it's pretty poor that they end up being unsynchronised by the control room with the signals. Bear in mind that one of the substantial Smart Motorway costs is a fully manned control room with the CCTV displayed on a video wall in front of the operator. Incidents should be able to be signalled in seconds.

Is MIDAS seen as unnecessary where there is CCTV ?

Now it's been many years since I was in a motorway control room, in fact so long ago that it was operated by the police rather than the road authority. But we did notice that those staffing it were by mo means the sharpest pencils in the pencilbox, and we then discovered that the position was regarded as something of a sinecure for those officers who were no longer fit for or capable of duty out on the street. I wonder how things have moved on.

[Bendo]

Sounds like someone needs to invent a system of motorway incident detection and automatic signal activation. I can't believe it hasn't been done before now.

To be fair it should have been done before these HSR / ALR schemes (I'll refrain from calling them SMART motorway as evidenced time and time again, they are anything but) were implemented as widening on the cheap.

[Brenley Corner]

Sounds like someone needs to invent a system of motorway incident detection and automatic signal activation. I can't believe it hasn't been done before now.

To be fair it should have been done before these HSR / ALR schemes (I'll refrain from calling them SMART motorway as evidenced time and time again, they are anything but) were implemented as widening on the cheap.

Errr....I think Richard may have been referring to MIDAS which has been active on the M25 for at least a decade if not more....

And no-one is denying is is a cheaper way of gaining more capacity, but when you have chronic capcity issues and limited public funds then it becomes your preferred option by default.

[Bendo]

[And no-one is denying is is a cheaper way of gaining more capacity, but when you have chronic capcity issues and limited public funds then it becomes your preferred option by default.

And all is well with the world, until a minibus full of school kids breaks down, the SMART systems fail to detect it and an inattentive HGV driver ploughs into the back of them.

Dramatic, perhaps but is it likely to happen? Given the number of reported failures on SABRE alone, where people have come across broken down vehicles with no indication whatsoever on the signage and this most recent one where there are police plus others in attendance so must have been stopped a while yet HSR still in place.

[andrewwoods]

I'll refrain from calling them SMART motorway as evidenced time and time again, they are anything but

It's SMART, as in 'ow, that really smarts'

[RichardA35]

[And no-one is denying is is a cheaper way of gaining more capacity, but when you have chronic capcity issues and limited public funds then it becomes your preferred option by default.

And all is well with the world, until a minibus full of school kids breaks down, the SMART systems fail to detect it and an inattentive HGV driver ploughs into the back of them.

Dramatic, perhaps but is it likely to happen? Given the number of reported failures on SABRE alone, where people have come across broken down vehicles with no indication whatsoever on the signage and this most recent one where there are police plus others in attendance so must have been stopped a while yet HSR still in place.

You've, perhaps unwittingly, cited a similar outcome to the "M40 minibus crash" which occurred when a vehicle crashed into the back of another which was stationary, but it was on a section with full hard shoulders.

[A9NWIL]

[And no-one is denying is is a cheaper way of gaining more capacity, but when you have chronic capcity issues and limited public funds then it becomes your preferred option by default.

And all is well with the world, until a minibus full of school kids breaks down, the SMART systems fail to detect it and an inattentive HGV driver ploughs into the back of them.

Dramatic, perhaps but is it likely to happen? Given the number of reported failures on SABRE alone, where people have come across broken down vehicles with no indication whatsoever on the signage and this most recent one where there are police plus others in attendance so must have been stopped a while yet HSR still in place.

I can imagine the headlines now governments smart motorway system causes school children to die! They would be installing hard shoulders very fast along all sections of so called smart motorways!

[Arcuarius]

Sounds like someone needs to invent a system of motorway incident detection and automatic signal activation. I can't believe it hasn't been done before now.

To be fair it should have been done before these HSR / ALR schemes (I'll refrain from calling them SMART motorway as evidenced time and time again, they are anything but) were implemented as widening on the cheap.

As evidenced? Righto, because that stretch of road would be so much better without it...