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.