Tod Fitch <t...@fitchdesign.com> writes: > Quoted sections have been edited down to only show parts I am responding to: > >> On Mar 22, 2017, at 5:37 AM, Greg Troxel <g...@lexort.com> wrote: >> >> For highway=traffic_signals, the normal situation is that it's on a >> node, and affects all ways entering the node. Or it's on a way and >> affects both directions -- in my experience, when there are traffic >> lights not at an intersection, they are always for both directions (even >> though in theory they could be set up for one direction only). > > CalTrans has used semi-permanent traffic signals to control traffic > flow over damaged road sections. A light at each side of the damaged > area controls the sequentially one-way traffic through the damaged > area that has been reduced to one lane operation. I’ve seen these in > the Santa Cruz mountains, but the longest section of road I’ve seen > controlled this way was on the main road to Yosemite Valley where the > side of the mountain came down on the main roadway and the work > around, in place for several years, was to put some pavement on the > old single track railway grade on the other side of the river and put > two bridges in place to get traffic across and back. It maybe still in > place while but I’ve not been through there in several years. I know > they took a long time to decide what to do about the still unstable > mountain above the covered section of highway. > > So there are places with traffic signals away any intersections that > control traffic going into a one lane section. I guess a smart router > could guess that the transition of a road from two lanes to one lane > would count as an intersection but that seems an error prone > algorithm. Having a direction tag of some sort available does make > tagging this situation possible.
You are totally correct. I have seen two traffic signal sets near me, controlling access to a one-lane bridge and a road where one lane is washed out and the other alternates. I had forgotten about these. But, while we need a way to represent these, I think the notion that: stop not at a node is towards the node only, unless otherwise tagged to be both signals is both ways, unless tagged to be just one way is relatively sound, in terms of striking a balance between mapping ease and data consumers.
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