£300m traffic jam busting scheme made journeys longer, Highways England admits

[WHBM]

Nearly every controlled, signalised junction I’ve had the misfortune to encounter has at least some congestion attributable to the cycle of lights, and naturally sluggish traffic after moving off.

Sometimes the green cycle is so short, as the queue moves off so slowly that only half of it manages to move away from the roundabout.

Looking at the examples from Preston there, that was obviously designed as an urban link road, whether as 50, 60 or NSL. It was also designed to be free-flowing with roundabouts. It at least one of the shots, the roundabout was replaced with a signalised T-junction.

I just cannot comprehend why, when all it will do is add to queueing, stationary traffic, and more vehicle emissions, and added CO2 from the lights themselves.

I used to know an old engineer who was a brilliant signal optimiser. No Transyt computer package for him. he would stand at the edge of the junction for half an hour, cigarette in mouth, and make notes in his little notebook about timings to the second. Give it a couple of weeks after installation (not 12 months like TfL do) and he would nip over at various times of day, including weekends and evenings in his own time, to see if any further adjustment was needed. Normally not, of course.

[Bryn666]

There are still signals people who will stand at a controller and make real world adjustments but many authorities have it in their minds as its wasted hours because they believe what compoota tells them.

[Graham]

I don't think there are many schemes which have "only brought negative outcomes". You might not value the positives - generally reduced queueing on certain arms during peak periods - but to write them off completely is unhelpful.

I would suggest that my local motorway junction - M5 J9 - is an example where signalisation has only brought negative outcomes.

There is no benefit at peak times, because the motorway junction is clogged up anyway by traffic backing up from the A46 through Ashchurch.

And at non-peak times, most journeys are lengthened by virtue of waiting at a red light with no traffic going the other way.

[Berk]

Why bother implementing a scheme if it only brings negative outcomes?? It would be better not to spend the money at all, seriously.

I don't think there are many schemes which have "only brought negative outcomes". You might not value the positives - generally reduced queueing on certain arms during peak periods - but to write them off completely is unhelpful.

Perhaps, but these schemes, like smart motorways, seem to have soaked up a lot of road spending over the last 15 years. And they haven’t helped to maintain, or reduce travel times, just helped a number of people turn left, or right more easily at junctions.

I firmly believe that junctions should give priority to the dominant flow(s), as that should allow time and space savings for turning or crossing traffic.

[Bryn666]

Err these signal junctions that HE are now admitting haven't worked are doing exactly what you say already or they wouldn't have been built.

The lesson here is that people who don't understand traffic flows are taking hypothetical computer models at face value and then being shocked when reality operates totally differently.

Someone told me the phrase "Garbage In Gospel Out" for these things.

[jackal]

Looking at the report a little more, there are some interesting outliers:

Table 3-7 Schemes identified as journey time outliers (all adverse)

A5-A49 Preston Boats
Major
The scheme introduced signals on the roundabout between
the A5 and A49. The A5 through movement and A5 east to
A49 movement have very high flows, but now these are held
back by signals, causing large journey time dis-benefits which
far outweighed the benefits the scheme brought to minor flow
movements.

M6 Junction 23
Minor
The scheme widened the central section of this hamburger
roundabout, and now moves the majority of traffic through the
centre of the junction, beyond the capacity of the central road.
As such there are large dis-benefits to all movements through
the hamburger.

A1 Southoe
Safety Cameras Minor
This speed camera and speed limit reduction scheme did
forecast a journey time dis-benefit but the dis-benefit was
heavily underestimated. As the speed limit was reduced over a
long distance (over 1.8 miles) there was a substantial change
to journey times. However, in terms of safety impacts this was
a positive scheme due to the large reduction in collisions on
this route.

Journey time disbenefits are £2.54m at Preston Boats, £1.48m at J23, and £1.74m at Southoe... just in the first year. And we wonder why our productivity lags the French and Germans.

https://assets.publishing.service.gov.u ... _draft.pdf

[Berk]

Yes, that’s right. I think the Southoe scheme is far too long. It should end as close as possible to the Bell pub (just after the bend). In fact, it continues at least another ¾-mile, past some workshops. That extent is totally unnecessary.

I’m not suggesting the scheme as a whole is unnecessary. But some thought should’ve been given to allowing a smoother transition to the Buckden village limit on the A1. The 50 limit continues southbound for another 350 yards or so beyond the roundabout.

It would’ve been clearer and simpler if it ended immediately at the southbound exit, and the 60 limit took over from there, rather than having to mentally negotiate two limits. The same could also be said of the Sandy/Beeston/ Caldecote limits 20 miles or so further south.

[Berk]

To be perfectly honest, you could ‘design away’ the Southoe bends very easily for about £10m, as has been done in many other places. Even the Elkesley scheme only cost around £6m.

Why can’t HE sort themselves out and fix it??

[dcrc2]

A1 Southoe
Safety Cameras Minor
This speed camera and speed limit reduction scheme did
forecast a journey time dis-benefit but the dis-benefit was
heavily underestimated. As the speed limit was reduced over a
long distance (over 1.8 miles) there was a substantial change
to journey times.

It's difficult to fathom how they managed to underestimate this. If you introduce a 60 limit with average speed cameras, then, clearly, that's going to result in traffic travelling at (at most) 60. How is it even possible to get this wrong?

[RichardA35]

A1 Southoe
Safety Cameras Minor
This speed camera and speed limit reduction scheme did
forecast a journey time dis-benefit but the dis-benefit was
heavily underestimated. As the speed limit was reduced over a
long distance (over 1.8 miles) there was a substantial change
to journey times.

It's difficult to fathom how they managed to underestimate this. If you introduce a 60 limit with average speed cameras, then, clearly, that's going to result in traffic travelling at (at most) 60. How is it even possible to get this wrong?

The original forecast was good enough to obtain the funding and a selection of viable schemes to spend the available money is what was wanted at the time....

[jackal]

Surely there should be more accountability on the part of the consultants. It seems tantamount to fraud to come up with such wildly optimistic estimates that the net effect of an entire 48 scheme congestion-busting programme is to increase congestion. There are international precedents, e.g.: https://www.wsj.com/articles/aecom-unit ... 1442826365

[Bryn666]

Surely there should be more accountability on the part of the consultants. It seems tantamount to fraud to come up with such wildly optimistic estimates that the net effect of an entire 48 scheme congestion-busting programme is to increase congestion. There are international precedents, e.g.: https://www.wsj.com/articles/aecom-unit ... 1442826365

I'm sure my views on the antics of HE and the big name consultants are well documented elsewhere. A lot of jobs for the boys whilst actual desperately needed schemes never happen.

[AndyB]

The problem with signalised roundabouts is that at all but the quietest times, the roundabout functions as a single junction. To prevent buildup at the next stop line on the circulation, traffic can be held for nothing to join the roundabout on one arm because that arm is linked to another arm which has a specific demand.

Consider the most basic model - four arm roundabout, let's call the exits ABCD starting from the top of the roundabout. Normally you would have traffic from C being able to go to D or A and traffic from A going to B or C while traffic from B and D have to wait, and traffic going A->D or C->B have to stop on the roundabout, and vice versa.

A demand comes in for arm B but not for arm D. In theory, and at night the lights may well be programmed to do this anyway, you could let traffic from A onto the roundabout and hold them at entry B for traffic from B to go as they please, but in practice the lights will clear for traffic from D as well so that if any appears while B has green lights, they can clear the junction.

[fras]

The problem with signalised roundabouts is that at all but the quietest times, the roundabout functions as a single junction. To prevent buildup at the next stop line on the circulation, traffic can be held for nothing to join the roundabout on one arm because that arm is linked to another arm which has a specific demand.

Consider the most basic model - four arm roundabout, let's call the exits ABCD starting from the top of the roundabout. Normally you would have traffic from C being able to go to D or A and traffic from A going to B or C while traffic from B and D have to wait, and traffic going A->D or C->B have to stop on the roundabout, and vice versa.

A demand comes in for arm B but not for arm D. In theory, and at night the lights may well be programmed to do this anyway, you could let traffic from A onto the roundabout and hold them at entry B for traffic from B to go as they please, but in practice the lights will clear for traffic from D as well so that if any appears while B has green lights, they can clear the junction.

And thank God we no longer have signals at Crewe Green roundabout !! Just what caused this mania for signals at roundabouts a few years ago ? All a signalised roundabout does IMHO, is share out the misery and also reduce the capacity of the junction anyway. It cannot be otherwise, as there is always a period between changes when nothing moves that wasn't there before.

[KeithW]

Yes, that’s right. I think the Southoe scheme is far too long. It should end as close as possible to the Bell pub (just after the bend). In fact, it continues at least another ¾-mile, past some workshops. That extent is totally unnecessary.

I’m not suggesting the scheme as a whole is unnecessary. But some thought should’ve been given to allowing a smoother transition to the Buckden village limit on the A1. The 50 limit continues southbound for another 350 yards or so beyond the roundabout.

It would’ve been clearer and simpler if it ended immediately at the southbound exit, and the 60 limit took over from there, rather than having to mentally negotiate two limits. The same could also be said of the Sandy/Beeston/ Caldecote limits 20 miles or so further south.

Trouble is there were a number of fatal accidents on that stretch as a result of vehicles going into bend far too quickly and encountering other vehicles joining or crossing the road at the flat junctions for Diddington and Southoe. If you only start the limit just south of that bend there will still be northbound cars doing at least the NSL as they enter the bend. Yes its annoying when you know the road but if you are encountering it for the first time its all too possible to get it horribly wrong. Imagine doing 70 mph and encountering someone entering or crossing the road here.
https://www.google.co.uk/maps/@52.26377 ... 6656?hl=en

The Highways Agency, as it then was, found itself getting a lot of flack because of the number of fatalities on this stretch. Ideally of course that part of the A1 should be upgraded but it doesn't look likely to be funded soon if at all.
https://www.huntspost.co.uk/news/highwa ... -1-1832839

As to the transition past the Buckden roundabout the same applies. You dont want northbound cars approaching the roundabout at 60 mph, the 50 limit was already there when the Southoe stretch was NSL and of course northbound there are residential properties with direct access to the A1.
https://www.google.co.uk/maps/@52.29057 ... 6656?hl=en

[WHBM]

Surely there should be more accountability on the part of the consultants. It seems tantamount to fraud to come up with such wildly optimistic estimates that the net effect of an entire 48 scheme congestion-busting programme is to increase congestion. There are international precedents, e.g.: https://www.wsj.com/articles/aecom-unit ... 1442826365

I'm sure my views on the antics of HE and the big name consultants are well documented elsewhere. A lot of jobs for the boys whilst actual desperately needed schemes never happen.

Not going to stop me chiming in though ! The No 1 skill of a consultant is to please the client sufficiently that you get the next job coming along as well. So you carefully find out what they want, and then write that up in fancy prose as if you had discovered these facts yourself. No 2 skill is to absolutely maximise your revenue and billing from the project, where there are 101 ways to justify beating the client's consulting budget (provided you stay within the No 1 skill).

[AndyB]

The problem with signalised roundabouts is that at all but the quietest times, the roundabout functions as a single junction. To prevent buildup at the next stop line on the circulation, traffic can be held for nothing to join the roundabout on one arm because that arm is linked to another arm which has a specific demand.

Consider the most basic model - four arm roundabout, let's call the exits ABCD starting from the top of the roundabout. Normally you would have traffic from C being able to go to D or A and traffic from A going to B or C while traffic from B and D have to wait, and traffic going A->D or C->B have to stop on the roundabout, and vice versa.

A demand comes in for arm B but not for arm D. In theory, and at night the lights may well be programmed to do this anyway, you could let traffic from A onto the roundabout and hold them at entry B for traffic from B to go as they please, but in practice the lights will clear for traffic from D as well so that if any appears while B has green lights, they can clear the junction.

And thank God we no longer have signals at Crewe Green roundabout !! Just what caused this mania for signals at roundabouts a few years ago ? All a signalised roundabout does IMHO, is share out the misery and also reduce the capacity of the junction anyway. It cannot be otherwise, as there is always a period between changes when nothing moves that wasn't there before.

However, once the primary flow on a roundabout is constant enough to cause blocking back on the side road, it has ceased to function as a junction. The traffic on the side roads needs the opportunity to get onto the circulating carriageway, which traffic lights can force.

[KeithW]

However, once the primary flow on a roundabout is constant enough to cause blocking back on the side road, it has ceased to function as a junction. The traffic on the side roads needs the opportunity to get onto the circulating carriageway, which traffic lights can force.

Which is why Fiveways roundabout on the A11 was signalised, the constant stream of traffic on the A11 after it was dualled made it almost impossible to get onto the roundabout from the A1101. A11 users now know what it feels like to have to wait their turn.

[lefthandedspanner]

Surely there should be more accountability on the part of the consultants. It seems tantamount to fraud to come up with such wildly optimistic estimates that the net effect of an entire 48 scheme congestion-busting programme is to increase congestion. There are international precedents, e.g.: https://www.wsj.com/articles/aecom-unit ... 1442826365

I'm sure my views on the antics of HE and the big name consultants are well documented elsewhere. A lot of jobs for the boys whilst actual desperately needed schemes never happen.

Not going to stop me chiming in though ! The No 1 skill of a consultant is to please the client sufficiently that you get the next job coming along as well. So you carefully find out what they want, and then write that up in fancy prose as if you had discovered these facts yourself. No 2 skill is to absolutely maximise your revenue and billing from the project, where there are 101 ways to justify beating the client's consulting budget (provided you stay within the No 1 skill).

And No. 3 is to lay all the blame at the contractors' feet if it goes wrong due to faulty design / poor planning / etc.

[Vierwielen]

And then you have full-time traffic lights at locations where, at most, you would only want peak time control, such as here -

The Queen's Roundabout in Farnborough was one such pinch-point scheme turning a free-flowing roundabout (other than 16:30-18:00 when the business park kicks out) into a 24/7 congestion point.

Most infuriatingly, the sequencing of the lights is such it is virtually impossible to get around the roundabout without having to stop at every set

Not to mention that the 70MPH limit on the dual-carriageway Farnborough Road has been reduced to 50MPH on the approach and 60MPH for the rest......

One of the problems with this roundabout is splitting the west-bound traffic so that any traffic turning into Queens Gate Road does not interfere with the traffic continuing along Government House Road.