23 April 2010

Uncommon problems at Clapham junction

What would the person on the Clapham omnibus think about this? This junction has been exercising a few minds on the Lambeth Cyclists e-group.

It's the end of Cedars Rd, heading south towards the edge of Clapham Common. Motor traffic can only turn left (left lane) or right (right lane), but cyclists can go straight on, taking a recognised, signed cycle path across the Common. There's a nice prominent ASL, and without traffic it looks pretty straightforward (right).

But the traffic lights have recently been changed to add a left-filter, which kicks in several seconds before the general green (right).

So if you're going straight on, and you've positioned yourself in the ASL at red anywhere except the far right-hand side (a natural thing to do if you don't know the junction, with the entry to the ASL being on the left - see picture right), you're in trouble: left-filtering traffic behind you will be hooting you to get out the way, and hustling past. It's a nasty little example of designed-in conflict.

You can't solve it by adding a straight-ahead cycle filter simultaneous with the left-filter, because there's left-to-right sideways traffic in front of you in that phase.

You could add symbols to the ASL, splitting it into two with a prominent left arrow in the left half, and straight-on-and-right arrows in the right, but that might be thought too complicated. Similarly, you could redraw the ASL half-size as a box at the top of the right-hand lane, though again that might be thought confusing.

Or you could just acknowledge your mistake and remove the left filter.

Or you could solve it the London way (right): render the ASL unusable by having traffic routinely block it anyway.


  1. 1. The ASL feed should go central as anything that encourages bikes to go up the LHS of turning traffic is dangerous.

    2. even if bikes stay in the RHS, they will get clipped by any turning bus.


  2. Another TfL cycling fail.

    If they had actually look at the cycle infrastructure they would have moved the fron of the ASL forward (so you would be clear of left filtering traffic), and put the approach lane in the middle (as suggested above) like Baylis Road by Waterloo is.
    But they never consider the cycle set out until much later (if at all).

    If I was sitting in the ASL waiting to go straight on across the common, no amount of hooting would make me move until I had a green light. Maybe the driver might complain about the setup then as well.

  3. I have one of these on my commute in Cambridge. I know to sit in the right-hand side of the ASL (to make it more complicated, the lights aren't always phased) but every couple of weeks a group of tourists on rented bikes stop in the left hand lane, then get really hot and bothered.

    Agree with SteveL's (1) and (2)

  4. From Queen's Gate into Hyde Park there is an ASL with a central access lane -- cars can't go straight on here (only left and right), but there is no filter.