Ideas to expand traffic signals

[Minh_Nguyen (Minh Nguyễn)]

@ManuelB701

Naturally, there is the limitation that it doesn’t work on highway=traffic_signal in the middle of a junction so this sort of tagging only works in the grand scheme on micromapped traffic signals. However, it is entirely valid when used in the middle of a linear way.

Although I think the historical concerns about mapping highway=traffic_signals on intersection nodes have been overblown, micromapping them at stoplines is clearly where we’re headed. It means both routers and renderers will need to do some postprocessing to reassociate the traffic signals with the intersections. Good thing OSRM recently released proper support for traffic_signals:direction=*! But some cases will always be harder without something to explicitly associate the traffic signal node with the intersection node:

@Minh_Nguyen

This isn’t perfect; sometimes the stop line is associated with more than one upcoming intersection node. For example, northbound traffic at this intersection waits for traffic on East Kemper Road, not Zind Lane:

The main pain point I have with traffic signals at the stopline is that there can be a many-to-many relationship between roadway centerlines and stoplines, a many-to-many relationship between stoplines and signal heads, and even a many-to-many relationship between lanes and stoplines.

@Minh_Nguyen

For example, in the U.S., when the cross street comes in at an angle, the stop line is often staggered lane by lane. Some mappers place the highway=traffic_signals node at the average of all the lanes’ stop lines; others at the average of only the through lanes’ stop lines; others at the nearest or farthest stop line; and still others at none of the above.

Explicit road marking ways can help to disambiguate the situation for other mappers and for renderers, if not for routers:

For lack of an established approach for tagging the roadways, I’ve experimented with micromapping traffic signal gantries and individual signal heads, especially at an unconventional interchange like a SPUI or superstreet. My first attempts at this attracted some skepticism. It’s good to know that I’m not alone in wanting to micromap signalized intersections, and railway signaling might give us a reasonable model to follow. That said, I think it’s worth reassuring the community that this degree of micromapping won’t be a baseline requirement, at least not for a long time.