Displaced right turn/continuous flow junctions

The study of British and Irish roads - their construction, numbering, history, mapping, past and future official roads proposals and general roads musings.

There is a separate forum for Street Furniture (traffic lights, street lights, road signs etc).

Registered users get access to other forums including discussions about other forms of transport, driving, fantasy roads and wishlists, and roads quizzes.

Moderator: Site Management Team

User avatar
jackal
Member
Posts: 7549
Joined: Tue Jan 08, 2008 23:33
Location: M6

Displaced right turn/continuous flow junctions

Post by jackal »

In this junction type, one or more of the right turns cross before the main intersection, reducing the number of conflicts at that point. I know of two examples in the UK:

https://www.google.co.uk/maps/@51.60136 ... z?hl=en-GB

https://www.google.co.uk/maps/@50.48629 ... z?hl=en-GB

The Swindon example is discussed in this paper.

Any more?
User avatar
wrinkly
Member
Posts: 8986
Joined: Tue Mar 04, 2008 12:17
Location: Leeds

Re: Displaced right turn/continuous flow junctions

Post by wrinkly »

Are you only looking for signal-controlled junctions?

In the early 1960s at unsignalled rural junctions with minor roads, it was not unusual to have a triangular traffic island with two-way traffic on all three sides. I think it was a recommended layout in the equivalent of the DMRB in certain circumstances. Some that were built then have since been altered. In a sense a minor road junction with some spare space between the fences or hedges can naturally develop into such a junction. Here are two in one view near M6 J19:

https://www.google.co.uk/maps/@53.30789 ... a=!3m1!1e3
User avatar
Big L
Deputy Site Manager
Posts: 7517
Joined: Sun Nov 14, 2010 20:36
Location: B5012

Re: Displaced right turn/continuous flow junctions

Post by Big L »

Make poetry history.

Did you know there's more to SABRE than just the Forums?
Help with maps using the new online calibrator.
Add your roads knowledge to the SABRE Wiki.
User avatar
Chris5156
Deputy Treasurer
Posts: 16908
Joined: Thu Sep 06, 2001 21:50
Location: Hampshire
Contact:

Re: Displaced right turn/continuous flow junctions

Post by Chris5156 »

Surprised the big one on the Reading IDR hasn't been mentioned yet.
Peter Freeman
Member
Posts: 1390
Joined: Thu Aug 30, 2012 07:52
Location: Exits 9 & 10, M1 East, Melbourne, Australia

Re: Displaced right turn/continuous flow junctions

Post by Peter Freeman »

jackal wrote: ... reducing the number of conflicts at that point ...
... and, importantly, enabling 2-phase-only signalisation.
User avatar
jackal
Member
Posts: 7549
Joined: Tue Jan 08, 2008 23:33
Location: M6

Re: Displaced right turn/continuous flow junctions

Post by jackal »

I can see there are going to be some tricky definitional issues here. My intuitive sense is that there isn't really a main intersection with displaced right turns at the Reading IDR example, but rather a series of smaller intersections. On a micro scale this might also apply to wrinkly's unsignalized intersections.

That would at any rate make sense of the claim in the paper I cited that the Swindon example, opened in 2002, is the first in the UK.
Reading
Member
Posts: 2946
Joined: Mon Oct 19, 2015 14:50

Re: Displaced right turn/continuous flow junctions

Post by Reading »

Chris5156 wrote:Surprised the big one on the Reading IDR hasn't been mentioned yet.
Only because i was busy

It is also regularly abused - you see cars come down from the slip marked salvation army on your map and make an illegal right turn either straight across or at the yellow box to save having to go down and around the signalised roundabout under the flyover by the oracle.
Peter Freeman
Member
Posts: 1390
Joined: Thu Aug 30, 2012 07:52
Location: Exits 9 & 10, M1 East, Melbourne, Australia

Re: Displaced right turn/continuous flow junctions

Post by Peter Freeman »

Those UK examples are not really offset-right-turn continuous flow intersections (offset-left-turns in the USA), except for (marginally) Swindon. They predominantly enable advanced left turns. Useful, but not proper CFI's.

Melbourne, Australia has just opened its first implementation. It's a re-work of an existing and very congested traditional signalised crossroads. It is a CFI of the 'parallel flow' type, enabling advance execution of a right turn (southbound to westbound). Of the other three right turns, two have to do a P-turn and one (eastbound to southbound) is simply prohibited (alternative routes exist). The efficiency gain results from two-phase signal operation.

It's been operating for one week, so it's too early to say how well it's achieved its aims. I think it will.

https://www.youtube.com/watch?v=86X7XkBX7Vk

https://www.youtube.com/watch?v=kOtq2IW ... e=youtu.be
Last edited by Peter Freeman on Wed Aug 21, 2019 22:34, edited 1 time in total.
User avatar
Berk
Member
Posts: 9779
Joined: Fri Sep 10, 2010 02:36
Location: somewhere in zone 1

Re: Displaced right turn/continuous flow junctions

Post by Berk »

I find it notable the Swindon example has an effective ‘contraflow’ with both right-turning lanes parallel to each other giving the impression of ‘driving on the right’.
User avatar
jackal
Member
Posts: 7549
Joined: Tue Jan 08, 2008 23:33
Location: M6

Re: Displaced right turn/continuous flow junctions

Post by jackal »

Peter Freeman wrote: Sun Mar 24, 2019 09:47 Those UK examples are not really offset-right-turn continuous flow intersections (offset-left-turns in the USA), except for (marginally) Swindon. They predominantly enable advanced left turns. Useful, but not proper CFI's.

Melbourne, Australia has just opened its first implementation. It's a re-work of an existing and very congested traditional signalised crossroads. It is a CFI of the 'parallel flow' type, enabling advance execution of a right turn (southbound to westbound). Of the other three right turns, two have to do a P-turn and one (westbound to southbound) is simply prohibited (alternative routes exist). The efficiency gain results from two-phase signal operation.

It's been operating for one week, so it's too early to say how well it's achieved its aims. I think it will.

https://www.youtube.com/watch?v=86X7XkBX7Vk

https://www.youtube.com/watch?v=kOtq2IW ... e=youtu.be
The Swindon example is textbook CFI. The right turns cross over south of the main intersection, reducing the number of signal phases. I'm not sure how you could think right turns crossing over could be for the benefit of left turns?

The second (Torquay) example is essentially the same but more compact, so the crossover point is very close to the main intersection.
Peter Freeman
Member
Posts: 1390
Joined: Thu Aug 30, 2012 07:52
Location: Exits 9 & 10, M1 East, Melbourne, Australia

Re: Displaced right turn/continuous flow junctions

Post by Peter Freeman »

Your Swindon and Torquay examples are similar, and both ARE technically DRT-CFI's (USA DLT), but hardly classic. The classic DRT intersections originally constructed in Mexico City, and now with more in the USA, are crossroads not T's. Your example in Torquay can only exploit the advantages to a limited extent because (as you observed) the crossed-over section is not long enough: too little storage . This applies less to the Swindon example, and perhaps in both cases it's not a problem if the volumes are low.
Last edited by Peter Freeman on Wed Feb 12, 2020 13:17, edited 1 time in total.
Peter Freeman
Member
Posts: 1390
Joined: Thu Aug 30, 2012 07:52
Location: Exits 9 & 10, M1 East, Melbourne, Australia

Re: Displaced right turn/continuous flow junctions

Post by Peter Freeman »

Berk wrote: Sun Mar 24, 2019 16:32 I find it notable the Swindon example has an effective ‘contraflow’ with both right-turning lanes parallel to each other giving the impression of ‘driving on the right’.
You're right, and I'm not sure whether this would feel disconcerting. It's even more pronounced in the usual crossroads implementations where a free-left-turn lane runs alongside the crossed-over right-turn lane, making four parallel carriageways. Both internal ones of those four run between opposing flows in their adjacents.
User avatar
Bryn666
Elected Committee Member
Posts: 35755
Joined: Thu Jun 20, 2002 20:54
Contact:

Re: Displaced right turn/continuous flow junctions

Post by Bryn666 »

Peter Freeman wrote: Sun Mar 24, 2019 09:47 Those UK examples are not really offset-right-turn continuous flow intersections (offset-left-turns in the USA), except for (marginally) Swindon. They predominantly enable advanced left turns. Useful, but not proper CFI's.

Melbourne, Australia has just opened its first implementation. It's a re-work of an existing and very congested traditional signalised crossroads. It is a CFI of the 'parallel flow' type, enabling advance execution of a right turn (southbound to westbound). Of the other three right turns, two have to do a P-turn and one (westbound to southbound) is simply prohibited (alternative routes exist). The efficiency gain results from two-phase signal operation.

It's been operating for one week, so it's too early to say how well it's achieved its aims. I think it will.

https://www.youtube.com/watch?v=86X7XkBX7Vk

https://www.youtube.com/watch?v=kOtq2IW ... e=youtu.be
That looks like a hybrid of a CFI and Michigan Left type junction. I like it although I did notice the dreaded Melbourne Hook Turn still remains on the east-west route.
Bryn
Terminally cynical, unimpressed, and nearly Middle Age already.
She said life was like a motorway; dull, grey, and long.

Blog - https://showmeasign.online/
X - https://twitter.com/ShowMeASignBryn
YouTube - https://www.youtube.com/@BrynBuck
Peter Freeman
Member
Posts: 1390
Joined: Thu Aug 30, 2012 07:52
Location: Exits 9 & 10, M1 East, Melbourne, Australia

Re: Displaced right turn/continuous flow junctions

Post by Peter Freeman »

Bryn666 wrote: Mon Mar 25, 2019 05:20 That looks like a hybrid of a CFI and Michigan Left type junction. I like it although I did notice the dreaded Melbourne Hook Turn still remains on the east-west route.
Bryn, my mistake in linking to a video that dates from the planning stage. The first link does show a hook turn, but in a design revision it was deleted. That right turn is abolished: not even catered for by a P-turn. And the eastbound route through the intersection is actually single lane, not two as in that video, since the volume is quite low and it leads onto an already-congested shopping/restaurant street.

The northbound approach was also revised: it has 4 lanes ahead, one turn left, and one kerbside bus-lane/bus-stop. No walking across a traffic lane to get to the bus!

The second url shows the final, as-built design.
Peter Freeman
Member
Posts: 1390
Joined: Thu Aug 30, 2012 07:52
Location: Exits 9 & 10, M1 East, Melbourne, Australia

Re: Displaced right turn/continuous flow junctions

Post by Peter Freeman »

^ I don't even know what a Michigan Left Turn is. I know of many of these innovative flat turn types: P-turn, G-turn, Q-turn, Jug-handle, ... I know what some of them are, but not all. I remember when I lived in London in the 70's there were, on Cromwell Road eastbound, several whole-block run-arounds where you turned left-right-right to, in effect, go right at the next crossroads. I don't know whether they're still there.

The Punt Road CFI in Melbourne is rather a 'special'. The main (southbound-to-westbound) right turn only just precedes the real crossroad space, but then it has a significant length of westbound running before crossing over to the correct side. This space is not for storage: it flows simultaneously with E-W and W-E flows (though they get slightly interrupted).

The Parallel Flow design can be looked at as a reversal of the Displaced Right Turn. In other words, the crossover occurs after the turn, not before it. The easiest way to visualise this and see the similarity, is to picture this actual Australian layout being traversed by driving-on-the-right traffic.

The design takes advantage of un-utilised space on the NW corner. Otherwise it wouldn't fit. It seems to me that most DRT's and other CFI's need quite a lot of space, so whether they can fit depends very much on the exact local circumstances. This means that many will, in practise, be 'specials'.
Last edited by Peter Freeman on Mon Aug 29, 2022 03:09, edited 1 time in total.
ais523
Member
Posts: 1139
Joined: Tue Sep 08, 2015 19:52
Location: Birmingham

Re: Displaced right turn/continuous flow junctions

Post by ais523 »

The signage at the Swindon example seems rather inadequate to me. You're directing drivers onto what would be, in most junction designs, the wrong side of the road; and all that's there to indicate that is some road markings and a tiny "pass to the right" bollard. I'd expect at least "no entry" signs, rather than just NO ENTRY painted on the road.

The junction design seems like it could be viable, but we'd have to get better at telling drivers what to do when they're there.
User avatar
Berk
Member
Posts: 9779
Joined: Fri Sep 10, 2010 02:36
Location: somewhere in zone 1

Re: Displaced right turn/continuous flow junctions

Post by Berk »

Yes, I can’t really see the justification for that either. :confused:

There doesn’t seem to be anything to suggest they couldn’t have done it the right way.
User avatar
trickstat
Member
Posts: 8737
Joined: Sun Apr 06, 2014 14:06
Location: Letchworth Gdn City, Herts

Re: Displaced right turn/continuous flow junctions

Post by trickstat »

ais523 wrote: Mon Mar 25, 2019 12:52 The signage at the Swindon example seems rather inadequate to me. You're directing drivers onto what would be, in most junction designs, the wrong side of the road; and all that's there to indicate that is some road markings and a tiny "pass to the right" bollard. I'd expect at least "no entry" signs, rather than just NO ENTRY painted on the road.

The junction design seems like it could be viable, but we'd have to get better at telling drivers what to do when they're there.
Yes I think more should be done here.

My guess is that, at busy times, people unfamiliar with the junction may be a little confused but won't actually go down the wrong section of road because they would have likely seen cars going in the opposite direction from the area immediately to the left. However, I do think there is quite a high risk of someone getting it wrong before about 7 am or after 7 pm when there may be less traffic about to indicate where you should go.
User avatar
Berk
Member
Posts: 9779
Joined: Fri Sep 10, 2010 02:36
Location: somewhere in zone 1

Re: Displaced right turn/continuous flow junctions

Post by Berk »

I think this is only really a fail for at-grade junctions. If you consider some movements at grade-separated junctions (or ones that can be developed as grade-separated), sometimes a wrong-way movement can be easier to build, but give access to a right turn, for example.

I’ve often noted how in Spain, they seem to make right-turns there flow very easily, and left turns have a lot of spaghetti in some cases, but others just flow in the opposite direction. It may help when they have two-way slips (not something I’d want to encourage here).
User avatar
Bryn666
Elected Committee Member
Posts: 35755
Joined: Thu Jun 20, 2002 20:54
Contact:

Re: Displaced right turn/continuous flow junctions

Post by Bryn666 »

Berk wrote: Mon Mar 25, 2019 13:13 Yes, I can’t really see the justification for that either. :confused:

There doesn’t seem to be anything to suggest they couldn’t have done it the right way.
Other than by having a conventional junction you end up with extra stages and more congestion - this layout is fine, I'd have had a larger keep right sign but other than that the driver's eye perspective shows clearly to go ahead not first left.
Bryn
Terminally cynical, unimpressed, and nearly Middle Age already.
She said life was like a motorway; dull, grey, and long.

Blog - https://showmeasign.online/
X - https://twitter.com/ShowMeASignBryn
YouTube - https://www.youtube.com/@BrynBuck
Post Reply