[Talk-us] Motorway vs trunk classification for RI-4 and US-1 in Rhode Island

[Bradley White]

> There are cases where a freeway continues for some miles between the last
> elevated interchange and the first at-grade crossing, and adheres to
> Interstate standards (or nearly so) for nearly all of that distance. I'd
> tend to continue 'motorway' up to about where the first sign warns that the
> freeway is about to end (or, say, 3 km back, if I don't know where the
> warning starts).

This logic is, unfortunately, what leads to the tagging silliness you
describe going on with the Taconic State Parkway (which I agree is
tagged horribly, and is a fantastic case study of why trying to tag
every segment of divided, high speed road with a grade-separated
interchange as 'motorway' leads to bad tagging results).

There should be a continuity requirement for 'motorway' tagging,
especially in the U.S. where there is a robust, national standard for
what a freeway looks like. Two grade-separated interchanges in a row
on a divided highway should be an absolute minimum for tagging that
particular section as 'motorway'. Trunk roads *also* may be high
speed, divided roads with ramp access. If I get on a divided highway
via an on-ramp, and the next intersection I encounter 5 miles down the
road is an at-grade, was I really on a freeway? (Again: 'trunk' roads
_may_ be high speed, divided roads with ramp access) If so, then
tagging short segments near at-grade intersections as 'trunk' on what
is otherwise a 'motorway' makes perfect sense. If you have an at-grade
sandwiched between a sequence of grade-separated interchanges, there
is no non-silly way to tag it using this schema.

The simplest way to fix this problem is to require anything tagged as
'motorway' to be continuous (have a *minimum* of two grade-separated
interchanges in a row, ideally three) and to ramp access only, with
the main roadway being treated conceptually as a "ramp" for the sake
of determining where to switch between 'trunk' and 'motorway'. That is
to say, if you turn right onto a high speed, divided highway via an
at-grade intersection, it's not a 'motorway' until the first ramp
merges with the highway, _assuming_ that there is at least one other
grade-separated interchange afterwards.

This approach is about as on-the-ground as it gets, and does not rely
on "begin/end freeway" signage, which may or may not be present. An
aside: there are a handful of cases in California at least where
"freeway entrance" signage is posted at the on-ramps of two-lane,
grade separated highways, which do not meet the OSM standard for
'motorway' (CA 154/192, CA 108). I would therefore disagree with using
freeway begin/end/entrance signage to determine conclusively what
should be tagged as a 'motorway'.