Hamburger/Throughabout Controversy

[DB617]

A locally panned A4174 junction upgrade has come under even more scrutiny this week after a fatal crash involving alleged dangerous driving.

What has gone wrong for this throughabout scheme in Bristol? It is notably the first in the region, so a new layout to many drivers, but surely that cannot be enough to justify the foaming-at-the-mouth opposition to this type of junction in the surrounding area?

I suggest it is a combination of poor execution in the approach design, leading to it not being abundantly clear how the roundabout works (unfortunately GSV for the finished junction is unavailable but I can testify that there is not a lot of emphasis on the 'right lane for straight on' nor the fact the road layout has changed at all), but also driving standards just being really poor. To actually pick up dangerous driving charges on a throughabout, a driver would have to be approaching at inappropriate speed, not paying attention ('autopiloting'?) or just panic.

In any case, would South Gloucestershire be wise to cancel the remaining five roundabout slicing schemes on the A4174 in the face of possibly poorly-informed local opposition? In my eyes this falls into the same category of driver opposition as 'why build cycle paths when I never see anyone cycling on this 50mph road?'...

[WHBM]

The trouble with Hamburgers is they continue to have a proportion who cannot understand that to turn right they need to go left and follow the roundabout. Logical to the traffic engineer in us, but not intuitive to a proportion of drivers. Such junctions I'm familiar with continue to have occasional violations I see. I suspect following Sat Navs which just show an overall right turn has added to the issues.

[Chris5156]

In any case, would South Gloucestershire be wise to cancel the remaining five roundabout slicing schemes on the A4174 in the face of possibly poorly-informed local opposition? In my eyes this falls into the same category of driver opposition as 'why build cycle paths when I never see anyone cycling on this 50mph road?'...

They'd be wise to can the project in favour of replacing the roundabouts with properly designed signalised junctions. It would be more intuitive for drivers to have a conventional signalised crossroads than to try signalising a junction that is inherently not suited to it. Signalised roundabouts, throughabouts, hamburgers and bananabouts are a horrible compromise that's best avoided.

[DB617]

In any case, would South Gloucestershire be wise to cancel the remaining five roundabout slicing schemes on the A4174 in the face of possibly poorly-informed local opposition? In my eyes this falls into the same category of driver opposition as 'why build cycle paths when I never see anyone cycling on this 50mph road?'...

They'd be wise to can the project in favour of replacing the roundabouts with properly designed signalised junctions. It would be more intuitive for drivers to have a conventional signalised crossroads than to try signalising a junction that is inherently not suited to it. Signalised roundabouts, throughabouts, hamburgers and bananabouts are a horrible compromise that's best avoided.

Now there's a radical idea. I have to admit the Warmley roundabout is so ridiculously small that it seems to be more carriageway than island, at which point you've just got a crossroads with extra - apparently fatal - steps.

The thing is, SGCC clearly has some competence to have considered something beyond "extra lanes means more flow" so why choose this weird road layout over signals? Perhaps it's some misconception that roundabout > signals is a downgrade?

[Chris5156]

In any case, would South Gloucestershire be wise to cancel the remaining five roundabout slicing schemes on the A4174 in the face of possibly poorly-informed local opposition? In my eyes this falls into the same category of driver opposition as 'why build cycle paths when I never see anyone cycling on this 50mph road?'...

They'd be wise to can the project in favour of replacing the roundabouts with properly designed signalised junctions. It would be more intuitive for drivers to have a conventional signalised crossroads than to try signalising a junction that is inherently not suited to it. Signalised roundabouts, throughabouts, hamburgers and bananabouts are a horrible compromise that's best avoided.

Now there's a radical idea. I have to admit the Warmley roundabout is so ridiculously small that it seems to be more carriageway than island, at which point you've just got a crossroads with extra steps.

The thing is, SGCC clearly has some competence to have considered something beyond "extra lanes means more flow" so why choose this weird road layout over signals? Perhaps it's some misconception that roundabout > signals is a downgrade?

Possibly. Other reasons are that retaining the current shape of the junction is cheaper, because you're not moving kerbs around; and that the signalised roundabout with cut-throughs has become an accepted junction type in the UK so it has some legitimacy within the engineering establishment.

[DB617]

It may have gained some legitimacy, but I think the execution is lacking in many ways. Is there any particular section on throughabouts in DMRB/TSM or any documentation at all on standards? From first impressions at Warmley, it seems that SGCC's designers just applied their version of common sense to the signage and ended up with the usual Bristol smorgasbord of confusing white paint on the road which always seems to come too late. It seems to me that the design is far cry from the clear signage requirements for motorways and major roads in DMRB and TSM.

[Bryn666]

The trouble with Hamburgers is they continue to have a proportion who cannot understand that to turn right they need to go left and follow the roundabout. Logical to the traffic engineer in us, but not intuitive to a proportion of drivers. Such junctions I'm familiar with continue to have occasional violations I see. I suspect following Sat Navs which just show an overall right turn has added to the issues.

This is not helped by the fact that many hamburgers now actively encourage turning right in places they shouldn't as part of the design so eventually you'll be faced with one where you can't do that and it'll cause an autopilot moment.

The M6/A580 hamburger now makes you turn right onto the M6 from the A580 instead of using the loops either side. Quite why they haven't just built an underpass for the A580 instead of all this constant tinkering with the edges, it's as bad as Switch Island for that.

[KeithW]

Well I was rather sceptical when one was built at the junction of the A66 and A171 (Cargo Fleet Lane) but seems to have worked quite well

https://www.middlesbrough.gov.uk/parkin ... provements

[DB617]

It seems they work quite well with a roundabout above a certain diameter - a situation which also leaves few options for 'just converting to a crossroads'. Perhaps one of the issues at Warmley is that the roundabout was already so small that it's now a visually cluttered environment which appears - especially to drivers on the circulatory bits - like there are roads going in every direction?

[tom66]

If these roundabout/throughabout designs are such a bad idea, why do they keep getting built? Where's the engineering justification for these junctions over an enlarged crossroads, for instance?

[jnty]

It seems they work quite well with a roundabout above a certain diameter - a situation which also leaves few options for 'just converting to a crossroads'. Perhaps one of the issues at Warmley is that the roundabout was already so small that it's now a visually cluttered environment which appears - especially to drivers on the circulatory bits - like there are roads going in every direction?

Yes - I think this works for large junctions which are closer to the 'gyratory' category; folk may get the idea that they are sort of like a roundabout, but unfamiliar motorists will probably just be treating them as a confusing collections of lanes and just know that they have to follow the right one to get to the right place, just as they might for a GSJ. When it's smaller, they probably try to (not unreasonably) second guess it as a road feature they're used to - and whether they guess crossroads or roundabout, they'll have got it wrong.

[Bryn666]

If these roundabout/throughabout designs are such a bad idea, why do they keep getting built? Where's the engineering justification for these junctions over an enlarged crossroads, for instance?

In a nutshell, they're cheaper than GSJs and fit in the same footprint as a roundabout. Whether or not they'll actually work appears to be a secondary consideration.

They can work well if designed correctly but that's the rub, we have a skills shortage and civil engineers with no traffic background are now designing highways schemes because they understand kerbs and levels design.

Traffic is NOT water, despite the oft repeated comment. Fluid dynamics does not apply to turbulent traffic flows powered by hundreds of individuals.

[M4Simon]

If these roundabout/throughabout designs are such a bad idea, why do they keep getting built? Where's the engineering justification for these junctions over an enlarged crossroads, for instance?

In a nutshell, they're cheaper than GSJs and fit in the same footprint as a roundabout. Whether or not they'll actually work appears to be a secondary consideration.

They can work well if designed correctly but that's the rub, we have a skills shortage and civil engineers with no traffic background are now designing highways schemes because they understand kerbs and levels design.

Traffic is NOT water, despite the oft repeated comment. Fluid dynamics does not apply to turbulent traffic flows powered by hundreds of individuals.

The better hamburgers are those where there is sufficient room for clear signage at different parts of the junction. On a small diameter roundabout this is all but impossible, and the chances of the whole thing locking up is significant because the individual links are too small. Experience tells me that if you've got room for a roundabout with a cut through, you've probably got enough room to replace the whole thing with a large signal junction, especially as your roundabout needs to be signallised to work safely as a hamburger. A good signallised junction can offer higher capacity, as well as better provision for oedestrians and cyclists compared with a less intuitive hamburger.

As someone with a foot in both camps (I do both highway civils and traffic engineering). It is actually quite difficult to find people who have a working knowledge of both. I worked for a county highways department and as part of my training scheme, worked in both disciplines but these days people seem to progress in their career as either a highway engineer (civils, levels, drainage etc.) or as a traffic engineer.

I'm very familiar with trying to reconcile the thoughts of some traffic modellers (if we extend that lane by one vehicle we can get the model to work) with the traffic engineer saying yes, it'll work in theory but as you can't get a decent taper into it, no vehicle will ever use it. Meanwhile the highway engineer is saying that you haven't allowed enough width to get the retaining wall you'd need to allow that extra bit of lane and by the way, if you are going to build that safely, you'll need to shut the entire junction down for 8 weeks because of that layout.

Design is always a compromise between what you'd like to achieve versus available resources (land, money, political will etc.) Too many schemes get put in because of the view:
We need to do something.
This is something.
We'll do this.

Simon

[Micro The Maniac]

They'd be wise to can the project in favour of replacing the roundabouts with properly designed signalised junctions.

Disagree.

Signalised junctions in this country seem never to be fitted with flow control [*], meaning you get a red light when there is no conflicting traffic, and lengthy cycles which only encourages amber gambling.
* Actually, the purely empirical but very frustrating evidence suggests that an approaching vehicle triggers a red light, not a green.

Roundabouts work most of the time - if really busy, peak-only lights can help. If a needs analysis suggests conversion to throughabout, then perhaps the solution is grade-separating? I have yet to see an example of a throughabout/hamburger that really solves the problem.

[Micro The Maniac]

This is not helped by the fact that many hamburgers now actively encourage turning right in places they shouldn't as part of the design so eventually you'll be faced with one where you can't do that and it'll cause an autopilot moment.

While not a hamburger (as such) the Meadows Roundabout (A30/A331) now has a right-turn filter immediately before the gyratory! Even with the veritable cornucopia of traffic lights, this roundabout is a regular accident incident hot-spot.

https://goo.gl/maps/XAJvJLVmfYoFPTf38

[NICK 647063]

I think personally they need to be of a decent diameter to be useful….

Of the few I’ve seen most seem to be where a major road crosses say a B road, or like the A66 that meets the A174 but the A174 doesn’t cross…

The biggest test for me will be the A64 new A6120 Junction, it’s the first I know where 2 major primary routes will cross each other at one of these junctions, in fact speaking to the design team they actually had all on deciding which route A64 or A6120 would get the throughout straight through route, the A6120 route was chosen due to expected future growth but the A64 will actually have the higher through flow, also add in 2 new routes coming off into the future housing developments, for me having to build something more that a roundabout from day one kind of admits this particular junction should have been a GSJ from day 1, it will be interesting to see but personally when I look at it all I can see is a future accident hot spot.

[Bryn666]

This is not helped by the fact that many hamburgers now actively encourage turning right in places they shouldn't as part of the design so eventually you'll be faced with one where you can't do that and it'll cause an autopilot moment.

While not a hamburger (as such) the Meadows Roundabout (A30/A331) now has a right-turn filter immediately before the gyratory! Even with the veritable cornucopia of traffic lights, this roundabout is a regular accident incident hot-spot.

https://goo.gl/maps/XAJvJLVmfYoFPTf38

Another classic example of the "we must fit in all movements even if they will cause problems". This happens a lot with these sorts of design and just because the computer says it works doesn't mean reality matches it, as Simon mentions upthread.

[KeithW]

I think personally they need to be of a decent diameter to be useful….
Of the few I’ve seen most seem to be where a major road crosses say a B road, or like the A66 that meets the A174 but the A174 doesn’t cross…

The closest the A174 gets to the A66 is over a mile, did you mean the A171 perhaps ?

In that case it was possible because wholesale demolition that occurred when the A66 was built meant there was ample space to build a good sized throughabout. The original round about was considerably smaller.

[Peter Freeman]

They'd be wise to can the project in favour of replacing the roundabouts with properly designed signalised junctions. It would be more intuitive for drivers to have a conventional signalised crossroads than to try signalising a junction that is inherently not suited to it. Signalised roundabouts, throughabouts, hamburgers and bananabouts are a horrible compromise that's best avoided.

Well said!

... so why choose this weird road layout over signals? Perhaps it's some misconception that roundabout > signals is a downgrade?

I believe that misconception is standard for most UK drivers. Stopping at signals is considered to be an imposition and a waste of time. The misconception appears to be endemic in the UK road design profession too.

It seems they [hamburgers] work quite well with a roundabout above a certain diameter - a situation which also leaves few options for 'just converting to a crossroads'.

?!? Why would more space leave fewer crossroads options?

If these roundabout/throughabout designs are such a bad idea, why do they keep getting built? Where's the engineering justification for these junctions over an enlarged crossroads, for instance?

The justification doesn't exist. It's just become a British habit to keep building them. If it was such a good idea, they'd be built elsewhere: good ideas get copied. The basic roundabout was a good idea, so everybody builds them. Traffic signals were a brilliant idea - now used all over the world. A 4-level stack for motorways is a great idea, and is accepted as the gold-standard GSJ. Hamburger a good idea? It doesn't seem to have recruited many believers.

In a nutshell, they're cheaper than GSJs and fit in the same footprint as a roundabout. Whether or not they'll actually work appears to be a secondary consideration.

A signalised crossroads can "fit in the same footprint as a roundabout". If it's a small roundabout, then its footprint will accommodate only a small crossroads. A large diameter roundabout will release enough space to accommodate a large crossroads. In either case, the area is used more efficiently by a crossroads. Downside? - you might have to wait at a red signal, even at off-peak times. (Of course, at a fully-signalised roundabout or hamburger, you could have to wait 3 or 4 times, if turning right).

[Bryn666]

They'd be wise to can the project in favour of replacing the roundabouts with properly designed signalised junctions. It would be more intuitive for drivers to have a conventional signalised crossroads than to try signalising a junction that is inherently not suited to it. Signalised roundabouts, throughabouts, hamburgers and bananabouts are a horrible compromise that's best avoided.

Well said!

... so why choose this weird road layout over signals? Perhaps it's some misconception that roundabout > signals is a downgrade?

I believe that misconception is standard for most UK drivers. Stopping at signals is considered to be an imposition and a waste of time. The misconception appears to be endemic in the UK road design profession too.

It seems they [hamburgers] work quite well with a roundabout above a certain diameter - a situation which also leaves few options for 'just converting to a crossroads'.

?!? Why would more space leave fewer crossroads options?

If these roundabout/throughabout designs are such a bad idea, why do they keep getting built? Where's the engineering justification for these junctions over an enlarged crossroads, for instance?

The justification doesn't exist. It's just become a British habit to keep building them. If it was such a good idea, they'd be built elsewhere: good ideas get copied. The basic roundabout was a good idea, so everybody builds them. Traffic signals were a brilliant idea - now used all over the world. A 4-level stack for motorways is a great idea, and is accepted as the gold-standard GSJ. Hamburger a good idea? It doesn't seem to have recruited many believers.

In a nutshell, they're cheaper than GSJs and fit in the same footprint as a roundabout. Whether or not they'll actually work appears to be a secondary consideration.

A signalised crossroads can "fit in the same footprint as a roundabout". If it's a small roundabout, then its footprint will accommodate only a small crossroads. A large diameter roundabout will release enough space to accommodate a large crossroads. In either case, the area is used more efficiently by a crossroads. Downside? - you might have to wait at a red signal, even at off-peak times. (Of course, at a fully-signalised roundabout or hamburger, you could have to wait 3 or 4 times, if turning right).

In Blackburn we replaced a roundabout with a signalised crossroads which locals then successfully managed to keep crashing at because they couldn't possibly look before turning. The signals were set to have back to back right turns before resorting to gap accepting as this was the most efficient method of control. The crossroads also has more pedestrian infrastructure than the roundabout ever did.

If a simple crossroads causes people to crash into each other why we keep insisting on conflict heavy hamburgers is a real mystery.