Pedestrianise London

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Traffic flow in a new Parliament Square

So to continue on from Thursday’s look at the LCC’s new look Parliament Square, I wanted to look at how traffic would flow through the intersection.

Now this has nothing to do with the LCC’s design vs a purely Dutch design, as both would require a major resequencing of the traffic control lights so as to make the junction safe for cyclists and pedestrians.

In the UK, signal controlled motor traffic tends to be managed in one of two ways depending on the size of the roads in question. Either the north/south traffic goes, then the east/west, with turns happening at any time during the green phase giving way to oncoming traffic (or on a filter light), or each incoming direction is given an all-ways green phase in turn.

Both of these schemes make it difficult to fit in pedestrian phases. The usual solutions are to either add pedestrian boxes to the middle of the street and creating a two phase pedestrian crossing (bad for pedestrians and for utilising road space), or an all-way pedestrian green phase is added.

Now try to fit in cycle friendly phases too and you find that you have right turning bikes conflicting with left turning motors.

The solution (as always) can be seen overseas and is pretty simple. Give each direction their own light phase. Here’s this demonstrated on the Parliament Square mock-up:

As you can see, we have 3 light phases that serve all traffic movement. Each direction of movement for all modes has it’s own phase combined with that of the opposite direction.

What this means is that we need to have separate left and right turning lanes for motor traffic as they need to given a green signal in different phases.

For example, if we look at the right/left turn phase as coming from the bottom of the picture, the right turn motor traffic lane is given a green signal at the same time as the bikeway is given a right turn signal, at the same time as the pedestrian crossing is given a green signal.

This is important. It means that all three modes of transport are given the same priority across the junction, it doesn’t matter which mode I use, I have to wait the same amount of time to get a green signal to proceed.

The dual t-junction in the above visualisation actually makes it pretty easy to implement such a system. If we were to instead have a single cross road, the number of turning lanes and the timings of the lights become more complex, something which I hope to investigate in a future blog post.

  1. pedestrianiselondon posted this