Sunday, 8 November 2015

Comparison of various intersection design types. Part 2. Protected intersection

You've seen the Copenhagen type of intersection last post. Now that I have explained what is wrong with it, let's go to an intersection that avoids the problems I mentioned. But first, watch this video: Protected intersection for cyclists


Note that the cycleways are now in red asphalt. The yield triangles are just showing that if the lights are not working or they go to flashing mode for whatever reason, the left-right flow goes first.

The design has major advantages over the Copenhagen Junction. It keeps cyclists in as little conflict with motor vehicles as possible. If you look closely, then you will notice that cyclists are to the right of the right turn lane. This would normally make people think that there is a huge problem. But there isn't. I will explain why in a little bit.

The corner refuge islands extend the protection of the cycle track in the intersection as well, creating continuity. You can make right turns on red without even needing a special exception to the no right turn on red signs or stopping. You make left turns in two stages, but you are protected if you have to wait. And the signal stages are much more flexible.

The intersection is much more intuitive, and easier to cycle through. The bend out is not sharp, and can be taken at something like 40 km/h+ if you wanted to. You also are in a position in that if you want to make a left turn by bicycle, you have no awkward turns.

The cycleway widths are also usually much wider than Copenhagen does. While Copenhagen has a 1.5-2.2 metre wide cycleway, Dutch protected intersections have 2-2.7 metre wide cycle paths. One way. For two ways they have 3-4 metre widths. Standard widths are usually 2.5 metres for one ways and 3.5 metre wide widths for two ways, 4 metres on primary routes. The buffer is also much wider. Minimum of 35 cm, preferable minimum of 1 metre, and standard buffer for a 50 km/h distributor is 1.5 metres, and for high speed or higher volume is about 2 metres. And it is a curbed buffer, a median. Often with things like plants, trees, grass, lamp posts, road signs, are in that buffer.

The traffic lights are programmed to separate the different directions. Here is an example signal stage:

The cyclists have their very own traffic lights and so do turning vehicles with protected prohibited signal staging. Pedestrians also have their own signals. The Netherlands does not have a signal to indicate that a lane with two directions you can go to from that lane has a protected movement in both directions, but Edmonton actually goes. A green ball and a flashing green arrow will do the trick. I do not believe that I have seen it used before for this purpose of providing the only left turn, and that the arrow will always be used if the left turn/thru lane has green, but tell me in comments if you know. 

The signal stages are rotated. If you rotate it to the right, then you will see that you will get the green light to proceed right after the signal stage that lets you go straight. Easy left turn. But note that during low volume periods where controlling the intersection like a two way stop would be done whenever sensors detect that this is possible with the given volumes and conditions. Full actuation would ensure that nobody would have to go through any signal stage that was not necessary. It also would not be a fixed cycle, any direction could get green at any time. Copenhagen intersections are usually fixed timing. 

Protected intersections have one flaw, and that is if there is a high volume of cyclists turning left (or diagonally, considering bidirectional cycle tracks. If that happens, over 15% of people make two stage turns, then simultaneous green is a good choice. If the intersection is too small for protected intersection, likewise simultaneous green gives you an easy way out of the problem. 

Be back for the simultaneous green blog post.

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