Weird ASL Design for Elephant

Ah, I missed this one. Repost maybe, but quality OP. On the 'chamfer', there are a couple of possibilities. My money would be on a mistake by the graphic designer who produced the illustration, as they often do. Either the 'chamfered' line should be broken, not solid, or it shouldn't be there at all.

If you read the TSRGD design specification (which was produced before they recognised certain problems that would rear their head at this location), you'll see that a lead-in lane is required for an ASL. As a lane on the inside of the left-turning lane would produce left hooks all the time, the design specifies a lane between the left-turning and first straight-ahead lanes, in this case the two nearside lanes. However, it is likely that cyclists would want to enter the ASL from the left-turning lane, too, e.g. if (wait for it) turning left. They haven't left enough room for a lead-in lane on that side, though, so that they might have included that chamfer to allow left-turning cyclists to enter the ASL on that side. In this case, the line should be broken, i.e. not part of the stop line.

ASL reservoirs are often implemented without any form of broken line, which means that no road user, including cyclists, may cross the first stop line. This is because engineers want to cram as many general traffic approach lanes in as possible. Some have therefore invented the 'chamfer', which of course is also against design guidance. It allows them to pretend that there's a stub of a lead-in lane without putting one in. If you just put a broken bit in of a straight-across stop line, this would cease to be a stop line at all for users of vehicles narrow enough to fit through that section, including motorcycles. (These are just some of the silly little technical/legal problems associated with ASLs.)

The other possibility is that that 'chamfer' shouldn't be there at all, perhaps as a holdover from an earlier design when the main lead-in lane wasn't in the drawing yet and the designer didn't understand the triangle's significance.

The idea was originally introduced partly because stop-line discipline by cyclists was always poor; people wanted to position themselves ahead of queues of motor traffic and filtered to the front beyond the stop line. The introduction of ASLs caused poor stop-line discipline by motorists, as many, if not most, stray into the reservoir ahead. Now what we have is the majority of ASLs being introduced at variance with design guidance, confusion about the rules (although of course there shouldn't be), lack of respect for those rules in the HC, and in practice not a lot of improvement on the ground, if any.

I personally don't waste time arguing for ASLs when campaigning on a traffic scheme. It's much better advice for cyclists to take their place in most short queues, anyway. For long queues, there generally is a better place near the front for them to position themselves than in the promised land of the ASL, which we think has a potential to increase unsafe filtering.

tynan's supposition is unlikely, although not impossible. I doubt that they would want to encourage cyclists to ride into the carriageway just ahead of the junction, ASL or not. There are facilities for moving from carriageway to footway called 'jug handles', usually found ahead of a toucan crossing (for peds and cyclists--'two can cross', geddit?) but not usually at junctions, more on links. It is possible that all crossings are toucan crossings, so that cyclists can ride all over the plaza-like footways (if they weren't permitted, it'd be an enforcement nightmare) and cross via the crossings. There also seems to be an on-footway cycle lane down the Walworth Road, which we would strongly discourage as a design, but that may be a mistake by the designer, too, as there doesn't seem to be a clear way indicated how to ride onto it from the carriageway.

If you find this sort of question interesting, cybertect, join the LCC's Cycle Planning and Engineering Committee, and you can discuss this sort of thing all day long. Enticing, no? ;)

Oliver
LCC