Re-modelled Junction. Comments please

[mwian]

Earlier this year the A470 Dolgellau by-pass was resurfaced and the junctions changed. The sections of 2 lane dual carriage way have had one lane closed off with white lines, the acceleration lanes removed and the junctions changed. In the last 6 weeks there have been 4 serious collisions with 2 deaths at the Bala road A494/A470 junction.
This is a link to a photo on facebook:-

https://scontent-b-lhr.xx.fbcdn.net/hph ... 1750_n.jpg

The silver car in centre of photo is waiting at Give Way markings to turn onto Bala Road. There are Give way markings at the sign you can see.

A photo of the same junction before improvement is here:-

http://www.sabre-roads.org.uk/wiki/inde ... -_1916.jpg

Since Friday (11th July) temporary traffic lights are in place.

[AndyB]

Right turners into side roads giving way to traffic exiting the side road is getting to be quite popular (see also Antrim-Ballymena, although it's a proper D2) - I think it's intended to help traffic in the side road.

[roadrunner]

Sounds like someone should be for the high jump!

[Benny]

Rhyds will be one to ask, this junction isn't far from his home town.

[Glen]

Turning right across multiple lanes (either in or out of a side road) is a higher risk manoeuvre, so removing the overtaking lane lowers the risk for right turners. A short overtaking lane that is only through the junction encourages higher speeds from overtaking traffic at the worst possible place.

The give way on the right turn lane in the central reservation is something that seems to be getting used more often and should create more opportunities for traffic exiting the side road to turn right. That in itself will do more to improve traffic flow in that direction, but there could be a safety benefit if it discourages rushed manoeuvres if more safe gaps are available.

Sounds like someone should be for the high jump!

Why, because there have been some accidents which may or may not be attributable to the new road layout?
What's more likely is that drivers haven't heeded the revised layout resulting in dangerous situations.
But we don't actually know what the accidents were of if they were involving turning traffic so we can't speculate either way.

Both the layout before and the layout after are safe if used correctly, but the new layout removed some of the risks of manoeuvres at the junction.

[roadrunner]

roadrunner wrote:
Sounds like someone should be for the high jump!

Why, because there have been some accidents which may or may not be attributable to the new road layout?
What's more likely is that drivers haven't heeded the revised layout resulting in dangerous situations.
But we don't actually know what the accidents were of if they were involving turning traffic so we can't speculate either way.

Both the layout before and the layout after are safe if used correctly, but the new layout removed some of the risks of manoeuvres at the junction.

4 serious accidents and 2 deaths in the last six weeks. Sounds like a lot of serious questions need to be asked about the engineering to me.

[PeterA5145]

Both the layout before and the layout after are safe if used correctly, but the new layout removed some of the risks of manoeuvres at the junction.

While apparently introducing some new risks

[Glen]

While apparently introducing some new risks

Which new risks? Other than drivers not adhering to the altered priorities - but that could be said of any layout - I don't see any additional hazards that have been introduced.

[nowster]

Was the junction considered dangerous before modifications?

[rhyds]

Previous to the new round of painting the junction was a regular right turn, and the scene of a few incidents (on average one every two or three months or so).

The new layout is the least intuitive piece of road engineering I've ever seen. They've lined the previously D2 sections to one lane aligned in the centre of the available space and the give way lines make no sense at all when you first roll up to them. It took me a fair bit of thinking and I'm a 28 year old with his faculties firing on all cylinders.

However its the timing that really caused all the fun and games. It must have taken an organisational genius to change the layout just before vast crowds of holidaymakers increased weekend traffic flows started.

The calls locally are for 50mph limits and roundabouts on both bypass junctions (Which will kill the freeflow), and with the carnage that's followed from this monumental engineering balls-up that's very likely to happen.

I'm surprised, considering the junction "improvement" has basically just been a new paint job that they haven't admitted their mistake and changed it back.

[rhyds]

Turning right across multiple lanes (either in or out of a side road) is a higher risk manoeuvre, so removing the overtaking lane lowers the risk for right turners. A short overtaking lane that is only through the junction encourages higher speeds from overtaking traffic at the worst possible place.

The traffic flow wasn't so high that you had regular overtaking on the D2 section you were turning across. The main benefit was for A494 (S) -> A470 (S) left turners as traffic on the A470 could move right to allow them to merge in.

[rhyds]

Why, because there have been some accidents which may or may not be attributable to the new road layout?
What's more likely is that drivers haven't heeded the revised layout resulting in dangerous situations.
But we don't actually know what the accidents were of if they were involving turning traffic so we can't speculate either way.

The accidents have been turning traffic.

http://www.dailypost.co.uk/news/north-w ... sh-7165249

http://www.dailypost.co.uk/news/north-w ... 70-7380944

http://www.dailypost.co.uk/news/north-w ... rt-7410120

[Glen]

The new layout is the least intuitive piece of road engineering I've ever seen. They've lined the previously D2 sections to one lane aligned in the centre of the available space and the give way lines make no sense at all when you first roll up to them. It took me a fair bit of thinking and I'm a 28 year old with his faculties firing on all cylinders.

So called "D1" junctions aren't that uncommon and are frequently designed as such from new.
Removing the overtaking lanes from this junction seems an entirely sensible thing to do as it reduces the hazard to traffic making both right turn movements.

The give way markings on the right turn lane aren't that common an arrangement, but seem to be increasingly used. Keeping the traffic turning into the side road in that position creates more gaps for traffic exiting the side road to turn right.

[rhyds]

roadrunner wrote:
Sounds like someone should be for the high jump!

Why, because there have been some accidents which may or may not be attributable to the new road layout?
What's more likely is that drivers haven't heeded the revised layout resulting in dangerous situations.
But we don't actually know what the accidents were of if they were involving turning traffic so we can't speculate either way.

Both the layout before and the layout after are safe if used correctly, but the new layout removed some of the risks of manoeuvres at the junction.

4 serious accidents and 2 deaths in the last six weeks. Sounds like a lot of serious questions need to be asked about the engineering to me.

It is a failure of highway engineering pure and simple. The old junction worked, the new one doesn't. Or is there an acceptable level of carnage during a changeover?

[rhyds]

The new layout is the least intuitive piece of road engineering I've ever seen. They've lined the previously D2 sections to one lane aligned in the centre of the available space and the give way lines make no sense at all when you first roll up to them. It took me a fair bit of thinking and I'm a 28 year old with his faculties firing on all cylinders.

So called "D1" junctions aren't that uncommon and are frequently designed as such from new.
Removing the overtaking lanes from this junction seems an entirely sensible thing to do as it reduces the hazard to traffic making both right turn movements.

The give way markings on the right turn lane aren't that common an arrangement, but seem to be increasingly used. Keeping the traffic turning into the side road in that position creates more gaps for traffic exiting the side road to turn right.

The junction at the other end of the bypass had been narrowed down to D1 southbound many years ago, with lane one for straight ahead and lane 2 for a right turn on to the A493. Northbound there were still two lanes through the junction, meaning you had an overtaking opportunity for that caravan you'd been stuck behind for the last 10 miles.

The problem isn't the D1, its the utterly confusing and unconventional give way arrangement at the actual turning point. It must have made sense on someone's desk or in a computer model, but add in confused tourists and holiday traffic and its a complete and utter disaster.

[Glen]

The traffic flow wasn't so high that you had regular overtaking on the D2 section you were turning across. The main benefit was for A494 (S) -> A470 (S) left turners as traffic on the A470 could move right to allow them to merge in.

But the overtaking lane ended before the acceleration lane merged in, so it wasn't usable for that purpose.

[rhyds]

The traffic flow wasn't so high that you had regular overtaking on the D2 section you were turning across. The main benefit was for A494 (S) -> A470 (S) left turners as traffic on the A470 could move right to allow them to merge in.

But the overtaking lane ended before the acceleration lane merged in, so it wasn't usable for that purpose.

But the flare in the roadspace didn't. Now you have white edge markings sending you straight down the middle.


At the end of the day these new markings are demonstrably dangerous. Of course Traffic Wales will never admit to that, having spend two weeks with 3 way temp lights putting them in. My answer would be to go back the simple, straightforward junction that was there for 30 years previous.

[PeterA5145]

While apparently introducing some new risks

Which new risks? Other than drivers not adhering to the altered priorities - but that could be said of any layout - I don't see any additional hazards that have been introduced.

Obviously the dead drivers didn't either.

As far as risk goes, the proof of the pudding is in the eating.

[Glen]

The accidents have been turning traffic.

But would they have happened with the previous layout, anyway? Did the change in layout contribute in any way?

While it's hard to establish exact causes from press photos, the one which resulted in the death of the motorcyclist seems to a all to common case of the car driver not looking properly and making a right turn across the path of the motorcycle. Something that has happened many times before and will continue to happen many times in the future with right turns of all types, whether single or dual, whether one lane or two.

[Glen]

At the end of the day these new markings are demonstrably dangerous.

Saying there have been some accidents doesn't demonstrate anything unless you have the details of what exactly the causes and contributing factors were.