[Talk-us] [Talk-us-newyork] Highway classification guidelines for New York State

[Richard Fairhurst]

Minh Nguyen wrote:
> You're right, I overlooked bicycle routing profiles. However, if I'm
> not mistaken, these heuristics only use the highway=* value as
> a fallback for when keys like lanes=*, maxspeed=*, and
> smoothness=* are missing.

Most OSM bike routing profiles broadly base their routing weights on the highway tag, in inverse order to what you'd expect for a car routing profile.

OSRM defaults:
https://github.com/Project-OSRM/osrm-backend/blob/master/profiles/bicycle.lua#L106-L115

Graphhopper defaults:
https://github.com/graphhopper/graphhopper/blob/master/core/src/main/java/com/graphhopper/routing/util/BikeFlagEncoder.java#L50-L62

Adjustments for lanes, maxspeed, smoothness etc. - and external data such as elevation - are then applied as a multiplier and/or limit on top of that. Most consumer-facing bike routing services follow this general approach. (cycle.travel's weightings are a bit more complex but that's another story!)

Generally the NY State guidelines you're proposing wouldn't conflict with this. I am a bit uneasy about applying highway=tertiary to unpaved roads. This is occasionally justifiable in Wyoming or on reservations etc., but would be anomalous for an east coast state. At the very least, the guidelines should have a strict injunction that if you do tag an unpaved road as tertiary, it needs a surface tag (and potentially tracktype/smoothness etc.).

The unclassified/residential distinction is well expressed and similar to how it's used elsewhere. In the US you do have the complicating factor that TIGER A41-class geometries were imported en masse as highway=residential, and often... aren't. So a router can generally assume that a rural highway=unclassified was deliberately tagged in the way of highway=unclassified in other developed countries (minor road, paved unless otherwise stated), whereas a rural highway=residential is "treat with extreme caution".

Any retagging of existing highway=unclassified to highway=residential would lose that information. I'd suggest, again, that the guidelines require any unpaved highway=unclassified to be given a surface tag, and that this is (at the least) strongly recommended for highway=residential.

Richard
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