Thursday, January 12, 2012

Bow Roundabout Redesign

Transport for London has proposed two alternatives for the Bow Roundabout, following the two fatalities of cyclists at the junction last year.

I won't go into the detail here as you can read about it here and officially here; suffice to say that the first and preferred plan involves on-carriageway cycle lanes with some physical separation from the main traffic lanes, and junction signals incorporating an 'advance' green signal enabling cyclists to set off before other traffic.  It only seems to cover one approach to the roundabout and one quarter of the roundabout itself.

What immediately jumps out is that this approach will protect cyclists against left-turning HGVs only if:
1. they manage to get to the front of the traffic queue before the lights change;
2. the advance stop box isn't blocked by motor traffic;
3. they get away smartly. How smartly they have to get away will depend on the light timing of course, but remember traffic flow at these junctions is very sensitive to signal timings so TfL will likely be setting them more for Eddy Merckx than your granny.

If you arrive at the junction with the lights green, the blue lane guides you to the left of the general traffic lanes and you emerge into the roundabout in the most vulnerable position. Ideally in this situation, if you're going straight on, you should be staying in the middle of the left-hand general traffic lane.

The other proposal is to remove one general traffic lane from the flyover and replace it with a cycle lane, separated from the motor traffic by islands at 40m intervals, described rather chillingly as "to deter motorists from using the cycle lane to undertake" . While this option has the obvious advantage that you don't have to negotiate the roundabout, there is the problem of getting onto the flyover, which requires crossing a couple of traffic lanes. They've quite neatly solved this by having what's basically a signalised crossing, allowing cyclists to cross the lanes from left to right while motor traffic is held at a red signal. (This is what they haven't done at Stockwell on the CSH#7, where to get into the cycle lane taking you round the gyratory you have to cut across two lanes of moving motor traffic at your leisure.) Again the question is timing: long phases will slow cyclists and encourage them to take the riskier option of the general traffic lanes instead. So TfL would need to allow frequent cycle phases. That combined with the removal of one flyover lane I imagine would have a significant effect on traffic flow. Will TfL go that far?

Of course, the flyover is no use if you want to to turn left or right up the A12. However, this is unlikely for most cyclists: the A12 is an unappealing prospect (and apparently cycling is prohibited, although there don't seem to be any signs prohibiting a cyclist from turning onto it at the roundabout).

LCC's proposed an alternative involving off-carriageway lanes and toucan crossings. This would seem safer (less danger of the HGV left-hook) and likely no slower than TfL's roundabout option. It might also be no slower than the flyover option, as that route would involve the same number of signalised crossings. It also has the advantage of facilitating pedestrians who fancy visiting the Bow Flyover Muccy D's.

Which option is best? I suspect it's a little early to tell, but so far I'm thinking the flyover option is the best of the TfL offerings, providing the light phasings are right, but I suspect they won't be. On the plus side, both schemes are a lot better than almost any other junction in London, but then the bar is pretty low. Let's not let two deaths be in vain: we should be insisting that conditions are as good as you'd get at Dutch junctions.

Remember to write to TfL to make your views known: looks like there's no formal consultation at this point but there's a contact page at the bottom of the scheme page.

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