Ignore intermittent or stop-and-go traffic signals

[1ec5]

The car profile treats any node tagged with highway=traffic_signals as a traffic light, presumably eligible for a penalty. However, not every highway=traffic_signals node would cause a car to stop for a significant amount of time. The auxiliary traffic_signals=* key provides a bit more nuance:

• traffic_signals=blinker has the same effect as a stop sign. I’m unsure whether that means it would take as long to traverse as an ordinary stoplight.
• traffic_signals=continuous_green by definition requires no waiting.
• traffic_signals=blink_mode and traffic_signals=emergency normally require no waiting.
• Even when traffic_signals=ramp_meter is activated, it has the same effect as a stop sign.
• traffic_signals=crossing is likely for footpaths, operated on demand either by button or sensor. It should have the same effect as any other crosswalk.
• I’m unsure what traffic_signals=tram_priority and traffic_signals=bus_priority indicate, but they might be intermittent as well.

taginfo says Valhalla supports this tag. Additionally, iD’s traffic light preset offers a combo box based on the most common values for the traffic_signals key.

/ref #3747 /cc @danpat

[willwhite]

What impact does this have or what is the buggy behavior that you're seeing here?

[1ec5]

In general terms, the impact is that OSRM is penalizing for things that should carry no penalty. For example, OSRM currently incorrectly penalizes many freeway on-ramps in California due to the presence of traffic_signals=ramp_meter. However, I haven’t done any measurements to determine how big of a problem this is in practice.

[1ec5]

I’d imagine the fix would be pretty simple: modify this line in the profile to avoid setting result.traffic_lights if traffic_signals is set to any value other than signals.

[1ec5]

A fix for this issue would complement the stop sign improvements in #2652.

/cc @chaupow

[emiltin]

It's a good idea to handle this, however i think a bigger improvement would be gained by avoiding double penalties at intersections, where multiple nodes are tagged with traffic_signal, but they change together so really should only incur the delay once. See #1250.

[1ec5]

I think most of the tags above would affect different roads than the ones affected by #1250 – such as freeway ramps for traffic_signals=ramp_meter – but I agree that both changes would be a significant improvement.

[ZLima12]

It's worth noting that traffic_signals=blinker does not necessarily mean that it's blinking red; if it blinks red, it acts as a stop sign, but if it blinks yellow, it acts as a yield sign (highway=give_way).