|This location, a large Simultaneous Green junction in Groningen, was chosen for this example because of its symmetry, making it easy to illustrate with arrows showing the routes that people take as they cross the junction. To simplify the diagram I have not shown the straight over routes by bike or the legal right turn against a red light routes. (Google map)|
Simultaneous Green design for cyclists works at both small and large traffic light junctions. This junction has many lanes of motor traffic, all of which is stopped while cyclists cross in one swift, safe and convenient movement. Junctions like this can also cater for vast numbers of cyclists. Note how the cycle lanes on several sides of the junction have more than one lane to cope with busy traffic. The cycle-path in the bottom right corner is five metres wide and has two northbound lanes combined with a southbound lane.
I drew this diagram in order to illustrate a common misconception amongst people who have never seen a simultaneous green junction in reality. It is often imagined that there will be many collisions between cyclists at the centre of the junction. If hundreds of cyclists really did try to ride perpendicular to each other directly through the centre of this junction at the same time then there would indeed be collisions, but that is not the reality.
Cyclists travel through curves
|The distance that A has travelled to|
reach the potential conflict point is
much shorter than the distance B has
to travel to do the same. The result
is no conflict in reality.
In the came of simultaneous green junctions, the arcs that cyclists travel through result in the potential conflict points not being reached all at once by all cyclists but in fact being spread through time and space from the point of view of any cyclist using the junction.
Consider cyclists A and B in the diagram. B has to ride considerably further than A to reach the same point. This means that for cyclists riding at similar speeds there simply is no conflict. He will in any case also expect to give way to A because the convention at these junctions is that everyone gives way to the right.
What's more, this is a simplification. My arrows do not show the exact lines of cyclist. In fact, the arcs used by individual cyclists at junctions like this vary enormously. While each cyclist turning left will start and finish in roughly the same place, these arrows should really be much wider in the centre.
While the cycle traffic lights are green, the entire area of the road junction is open for cyclists to use optimally. Faster cyclists often overtake slower cyclists while crossing diagonally. Negotiation takes place in that one party sometimes speeds up a little while another slows down. It is also straightforward to take a wider arc and therefore to go behind someone coming from your right.
The larger the junction, the more parallel routes are possible and the more efficient Simultaneous Green becomes both for cyclists and for other traffic as well because their total red time will be shorter with a simultaneous green layout than if cyclists cannot ride parallel and are required instead to follow each other in straight lines and cross twice.
|It's easy to pick up misconceptions from blogs,|
photos and videos online. Simultaneous Green
junctions are demonstrated on our cycling
infrastructure study tours.
Where it is not possible to remove traffic lights altogether or to make efficient routes for cyclists which don't include traffic lights for drivers, this is the best solution to make cycling both efficient and safe.
Read more about Simultaneous Green junctions (includes videos showing them in use)