[Tagging] Bridge highway=motorway classification

[marcel at dejean.nyc]

There seems to have been a certain number of edit wars over the
classification of various major bridges in New York City. As far as I can
tell, there's no consistent method used here right now for determining
whether a bridge is highway=motorway or highway=trunk or highway=primary.

One of the main criteria for what is a highway=motorway is that it has no
intersection controls on the main roadway (such as traffic-signals,
rotaries and roundabouts, and stop signs or stop markings). Bridges usually
don't have intersections, so that is not useful here. Another is that the
different directions are physically separated, this applies to most of the
bridges.

Another important factor is that highway= tags should apply where
reasonable to the whole road, not just a segment of it. Many of these
bridges were built to carry a major street, but when highways (
highway=motorways) were built later ramps were added only where convenient,
resulting in incomplete interchanges with them. Whether the bridges are
considered an extension of the highway or the major street might factor in.

I'm hoping we can come up with a reasonable method for determining what
highway= tag bridges like these should have.

In the below table I've catalogued some area bridges with varying
characteristics. The Carries column gives the street the bridge was built
to carry and its classification. The motorway_link column counts the number
of directions on the bridge that can be entered/exited (each counting 1)
from a highway=motorway. This ignores that not all lanes/roadways go to all
exits or all directions on the connecting motorway etc. Vehicles only is
whether bicycles and limited-use motorcycles are banned from the main
roadway as indicated by signage.
Bridge Carries motorway_link Separate roadways Pedestrian separation  Vehicles
only
Present tagging
Brooklyn Bridge <https://en.wikipedia.org/wiki/Brooklyn_Bridge> highway=primary
Adams St 3/4 Separate Separate Yes highway=trunk
<http://osm.mapki.com/history/way.php?id=432550255>
Manhattan Bridge <https://en.wikipedia.org/wiki/Manhattan_Bridge>
highway=primary
Flatbush Ave Ext 1/4 Separate Separate Yes highway=trunk
<http://osm.mapki.com/history/way.php?id=46189305>
Williamsburg Bridge
<https://en.wikipedia.org/wiki/Williamsburg_Bridge> highway=primary
Delancey St 2/4 Separate Separate Yes highway=motorway
<http://osm.mapki.com/history/way.php?id=40337615>
Queensboro Bridge <https://en.wikipedia.org/wiki/Queensboro_Bridge>
highway=primary
NY 25/NY 25A 0/4 Separate Separate Yes highway=motorway
<http://osm.mapki.com/history/way.php?id=198924625>
Triboro Bridge (Manhattan span)
<https://en.wikipedia.org/wiki/Triborough_Bridge#Harlem_River_lift_bridge_(NY_900G)>
highway=motorway
NY 900G (unsigned) 4/4 Separate Barrier Yes highway=motorway
<http://osm.mapki.com/history/way.php?id=5669174>
Willis Ave Bridge <https://en.wikipedia.org/wiki/Willis_Avenue_Bridge>
highway=primary
Willis Ave 2/2 One-way Barrier No highway=primary
<http://osm.mapki.com/history/way.php?id=5670524>
145th St Bridge <https://en.wikipedia.org/wiki/145th_Street_Bridge>
highway=secondary
145th St 0/4 No Curb No highway=secondary
<http://osm.mapki.com/history/way.php?id=5670765>
Washington Bridge <https://en.wikipedia.org/wiki/Washington_Bridge>
highway=secondary
181st St 4/4 Median Barrier No highway=motorway
<http://osm.mapki.com/history/way.php?id=33117565>
University Heights Bridge
<https://en.wikipedia.org/wiki/University_Heights_Bridge> highway=primary
Fordham Rd 0/4 No Barrier No highway=primary
<http://osm.mapki.com/history/way.php?id=19174360>
Broadway Bridge
<https://en.wikipedia.org/wiki/Broadway_Bridge_(Manhattan)>
highway=primary
US 9 0/4 Median Curb No highway=primary
<http://osm.mapki.com/history/way.php?id=126140593>
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