Monday 11 July 2016

A traffic light design which enables safe turns across traffic for everyone

Poor cycling infrastructure designs struggle when it comes to allowing cyclists to make turns across traffic (a left turn in continental Europe / USA) in a manner which is both convenient and safe. In some cases, designers simply don't really try and this results in such abominations as centre cycle lanes leading into advanced stop lines (bike boxes) on the ground. There are also examples of designs which are promoted quite hard but which don't really help people to cycle because they make turns inconvenient, dangerous or in some cases both inconvenient and deadly dangerous.

The new junction on the day it opened. The cycle-path widens
to nearly 4 metres in width to accommodate cyclists going
straight on as well as those turning left. Note traffic lights
for cyclists. The green for straight on is almost always lit.
This only goes red to allow cyclists to emerge from the right.
On the other hand, there are also good examples, though these are not necessarily so easy to find. Some designs improve both safety and convenience for cyclists. One solution for traffic lights which I'm particularly enthusiastic about because it has a very good track record is the simultaneous green junction, however there is no one design of junction which fits all locations and other good designs are possible.

This new junction demonstrates a very good way to design for asymmetric cycle traffic. In this case, almost all cycle traffic heads head straight on across the junction and they have a nearly full time green light. Only the relatively small number of cyclists who turn left are stopped by the traffic light in the video and this introduces only a short delay until it can stop all conflicting motor traffic and remove all danger from the left turn.

Crossing in the opposite direction is also convenient. Note that
right turning motor traffic is stopped when cyclists have a
green light and all straight on motor traffic is to the left of the
thick white line. There is no conflict in this direction either.
The old junction in this location featured on my blog in 2012. This already worked well, but it stopped cyclists heading straight on relatively frequently and did not allow for a left turn to be made by bicycle. The old junction was built on land and did not incorporate a bridge. The new bridge had to be built to enable re-opening a canal which was filled in decades ago and the new junction is on top of that bridge.

The Weiersbrug is one of six new bridges in Assen which began construction at the end of 2014. Five of those bridges are now complete and one remains to be built. I've been critical in the past of some aspects of the huge FlorijnAs project in Assen, but it has also brought improvements for cyclists in some locations, such as here.

Another view from another angle
This junction really does work very well for cyclists. The delays for a green light are minimal, and this partly is the result of the lights defaulting to red for everyone (cars, bikes, pedestrians) when there is little traffic and responding almost immediately to whoever comes along first. This video shows what it's like to go through this junction twice on a Sunday morning when there are few people about:

An older implementation of the same idea, with inadequate
lane sizes and not enough space to make the turn. This was
recently removed from the area around Assen railway station.
Not a new idea, but a top class implementation
The idea of cyclists waiting to turn left at a traffic light in this way is not in itself new. However, this new junction brings a level of refinement which makes it comfortable to use. This new junction works far better for left turning cyclists than did the an older implementation of the same idea which was recently removed from the railway station area of Assen.
The junction shown in the video with a blue arrow showing the route taken by left turning cyclists in the video. While cyclists make this maneouvre or any other across the junction which could result in conflict with motor vehicles, red traffic lights hold motorists to remove the conflict.
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Come and see
This new junction opened in May on the second day of a follow-up study tour. There is new cycling infrastructure to see every year in Assen and the programme changes each year to allow for what has changed. Future study tours, such as the tenth anniversary tour in September, will feature this junction amongst other pieces of new infrastructure.

True mass cycling, inclusive of all members of society, including children, older people and those with disabilities and where everyone makes all types of journeys by bike, is only possible with the very best cycling infrastructure. Be inspired by the best, not those things which really ought to be ignored.

1 comment:

Matt said...

Hi David, this is a very good example that could be used at T junctions everywhere, and I have proposed similar principles for the centre of Lewisham, for example. I also see that, ideally the cycle path should have been extended rather than using a cycle lane, but this proves that one can have greatly protected junctions and where infra could be prioritized if councils insist there is not enough money for cycle paths throughout. I understand that junctions tend to be the most dangerous areas and hence in greatest need of cycling infra.

The only thing would be to then work out how to handle cycling movements; my instinct (from learning from you and other bloggers) says cyclists usually do not need their own traffic lights but one could use give way lines or give way to the right or left rules (e.g. at the Blackfriars Bridge underpass!).