Thursday, 11 February 2016

Traffic Light Intersections Where you Can't Have Fully Separate Turning Stages

There are three main choices for what we can do if we need traffic lights. Simultaneous green, protected intersection and a simple roadway crossing where only a cycle path and or sidewalk crosses a roadway but motor vehicle-motor vehicle conflicts if any are not signalized. But not every location in Edmonton is likely to have the room for this, and not all locations have enough volumes of motor vehicles to warrant total separation in time.

These will probably be centered around the Downtown, University, Garneau and Strathcona areas, as well as surrounding neighbourhoods.

But how do you keep cyclists safe in areas where total separation with signals is not possible?

The solution is to have the best sightlines you can get, a good amount of time for cyclists to go ahead of the other traffic if possible, and removing as many conflicts as you can, even if you can't get them all nailed down.

Here is how the Dutch would approach this. They would use the model of the protected intersection if they can, this also helps with the left turn and allows right turns to be made on a red light. If the latter isn't possible otherwise and there is a cycle path or cycle lane which you could turn onto right around the nearside corner, then the Dutch use a "Rechtsaf voor fietsers vrij", meaning that you can turn right on red without stopping but after yielding to other traffic. The traffic light system also can have an advance green for cyclists, where you can get a headstart over motor traffic. Quite useful in many situations, especially if larger vehicles must remain. Not the 1 or 2 second head start for the most part, but something like 8-12 seconds or so is better. An eye level light and a regular full sized light is normal for this.

If you can't fit in the protected intersection, then you also have the option of setting the motor vehicle stopping line well back, something like 5 metres or more, plus the right turn on red sign and advance green, without having the waiting space for cyclists being a separate lane (or cycle track) than that for motorists. The so called bike boxes are probably worth a post about them in and of themselves, but for now, they should be extremely uncommon, if even ever present anywhere, and they should use a very long advance box, like 7.5 metres or more, a filtering lane, plus the advance green, not even 8 seconds, maybe 10 seconds or more, and possibly a longer clearance interval on the yellow and or red light, to make as good as it possibly can be, acknowledging that they should be extremely uncommon features if we ever do see them.

These arrangements also depend on drivers stopping at or behind the lines they need to be at. Setting the traffic light poles just in front of the stopping line, say 2 metres ahead, rather than perhaps 15 or 35 or something like that, means that you want to stay behind the line. These arrangements also depend on very low volumes (and speeds, no more than 50 km/h) of motor traffic, and preferably many more cyclists than motorists.

But these types of intersections without full signal protection should be very uncommon, and there should be easy ways to avoid them on your routes. The volumes and speeds must remain low in order for subjective safety by cyclists to remain high. And objective safety for that matter. TfL's early green, an odd variant of the bike box, has proven lethal, many times over. I don't know exactly how many but as best as I can tell, at least 5 dead in a few years. Which is a terrible safety record. Even one dead in it's entire history since a reconstruction means it needs rebuilding. It fails because of the volume of motor vehicles, and in particular a large number of trucks, and little time for cyclists to proceed ahead of the traffic because the pre green is way too short. Bow Roundabout (the intersection in question) easily has the space for separate turning stages. But no, TFL decides that motor traffic is more important than people.

That example shows how many factors have to come together for even an uncommon form of traffic control to work to an acceptable degree.


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