(my bold above)WHBM wrote: ↑Tue Apr 16, 2024 17:52 Collector Lanes are the opposite of Express Lanes on a North American freeway with four carriageways. The latter, in the centre, can go for miles without a junction. The Collectors on the outside have frequent on/off ramps to major streets.
A Transfer is where there is the ability to cross between one and the other, and a Rollover is where this is provided for all exchanging movements in both directions. I suppose the nearest UK equivalent to the latter is M4 J2. Here's one on the 401 in Toronto :
https://www.google.com/maps/place/Toron ... ?entry=ttu
The overlapping ramps at M4J2 are an impressive sight, especially for their time. Unfortunately, as you know, they're not a real transfer or rollover.
There is a pseudo-C/D road there though. It begins, on the A4 westwards, at the off-ramps leading down to Chiswick Roundabout, while Chiswick Flyover continues as Express Lanes. West of the roundabout, at ground level, A4 passes, and serves, some local roads (the final one being Lionel Road) before optionally ascending the ramp that takes it up to re-join the M4 express lanes. That's the end of the pseudo-C/D. A similar configuration occurs eastbound.
C/D start -
https://www.google.com.au/maps/place/Gr ... ?entry=ttu
C/D end -
https://www.google.com.au/maps/place/28 ... ?entry=ttu
That short piece of A4 almost qualifies as a C/D road because, westbound, it serves Chiswick Roundabout (A205/A406), followed by minor local roads and the A4 underneath the M4, and finally re-joins M4. Whether it's really a C/D road is doubtful though. Diverting onto a C/D road and using that instead of the express lanes should allow you to traverse its whole length uninterrupted by at-grade intersections in which you have no interest - and then rejoin.
The downwards wb off-ramp that spectacularly accompanies the upwards on-ramp is an exit only, to A4. It's not part of a rollover, but it is a braid. A4 wb then continues at ground level, serving Clayponds Lane, Ealing Road and Windmill Road before departing from the M4 line that it has shadowed up to that point. But it's definitely not a C/D there either, since it doesn't re-join.
Parallel cariageways that superficially resemble C/D roads are sometimes simply long ramps, often to facilitate a braid. They must rejoin express lanes, or offer the option to rejoin, in order to qualify as C/Ds.
C/Ds are common in the USA, but rare in Australia. Can anyone say where there are others in the UK?