Displaced right turn/continuous flow junctions

[Berk]

It’s an example of where lane markings are really vital to indicating the correct direction of travel. I wonder if something similar could’ve been done at Ardley/J10 (M40)??

[Peter Freeman]

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?

Yes Jackal, you're right. Swindon, Torquay and Reading, all topologically similar, ARE example of DRT T-junctions, and can operate with, essentially, two signal phases.

I was careless in only looking cursorily at your examples. I've now examined them properly. I think I was distracted by finding them to be T's, not four-arms. Interestingly, the UK article that you cite also, surprisingly to me, concentrates on T's.

While these are 'textbook' as you say, a full-blown archetypal classic DRT/CFI would be four-arm, with displaced turns on all four arms.

[jackal]

^ No worries, I can see that the three arm version may seem initially unfamiliar.

[Stevie D]

^ I don't even know what a Michigan Left Turn is.

A Michigan Left (which would be a Michigan Right in .uk or .au) is where you make a left turn by turning right and then making a u-turn ... or possibly continuing ahead through the junction, making a u-turn and then coming back and turning right. Apparently this is quite a common junction set-up in Michigan.

[Berk]

That’s known as a hook turn in Australia.

[lefthandedspanner]

Would the northern end of the M606 count?

[Peter Freeman]

^ I don't even know what a Michigan Left Turn is.

A Michigan Left (which would be a Michigan Right in .uk or .au) is where you make a left turn by turning right and then making a u-turn ... or possibly continuing ahead through the junction, making a u-turn and then coming back and turning right. Apparently this is quite a common junction set-up in Michigan.

OK, that's usually called a P-turn, in USA and AU (because in USA the shape is like a letter P). It is the type of turn recently implemented for 4 turns at two separate intersections on Hoddle Street / Punt Road in Melbourne. The innovative turn at Punt Road / Swan Street, the subject of my post a few days ago, is a Parallel Flow CFI. You turn right slightly in advance, and then run for some distance parallel to your turned-into road.

[Peter Freeman]

That’s known as a hook turn in Australia.

No, that's not correct.

AU's hook turn is used only in Melbourne, in order to eliminate obstruction of trams by right-turning vehicles. Right-turners pull over to the left within the intersection and wait there while straight-aheads (and perhaps trams) overtake them. At the end of the green phase, as the signals change to amber then red, the waiters complete their right turn (as quickly as possible!).

A sign (usually on a gantry) advises traffic on approach that the hook turn is mandatory. There were originally no special road markings, but in recent years many of the turns have had markings painted to define the waiting position.

Amazingly, it works reasonably well, despite being considered by many drivers (especially non-Melbournians) to be a confusing and worrying manoeuvre.

[Peter Freeman]

Would the northern end of the M606 count?

No.

[Peter Freeman]

I just discovered that the Parallel Flow Intersection that opened in Melbourne a year ago was NOT the first CFI in AU: the first one was actually in the City of Gold Coast, Queensland, in 2017. Its single displaced right turn is northbound on Route 3 dual carriageway, turning right into Salerno Street eastbound. The eastern displacement allows the turn to proceed simultaneously with both of Route 3's carriageways flowing.

It's worth noting that with DRT's and PFI's, any number of approaches may be treated. Melbourne's PFI and Gold Coast's DRT each treat only one approach. A full treatment, for a crossroads, would displace all four approaches, the resulting layout appearing rather complex at first sight. I'm unaware of whether any such full implementation exists: most treat just the two opposing highest flows.

Rather unusually, the displaced northbound carriageway in this example begins far back, at the preceding junction (to the south). This distance provides plenty of storage, and also means that no dedicated and signalised median-crossover is required. It's quite clever.

Here's a GE image -

[Peter Freeman]

Gold Coast Links:
http://www.mygc.com.au/australias-first ... w-open-gc/
https://www.youtube.com/watch?time_cont ... e=emb_logo

[Peter Freeman]

Australia's third CFI is under construction in south-central Sydney. It's at a skewed crossroads that is rather messily mixed up with a light-rail line. Two of its arms have crossovers on their approaches in order to displace the right turns. Traffic on the other two arms perform standard right turns.

EDIT: This intersection upgrade was completed, but not as a CFI. The finished layout looks rather similar, with strange crossovers of the tram lines existing, but it's not CFI. Reason: I don't know. It was part of a larger scheme that improved a route, composed of signalised surface streets, bringing M8 tunnel traffic north-eastwards. That scheme was strongly opposed by many Nimbies, so I think dropping its ending at a CFI was collateral damage from those protests. AU therefore still has only two CFIs: Gold Coast and Melbourne.