Handle modal filters

[dabreegster]

Particularly barrier nodes along a way. The clean approach might be to make these degenerate Intersections of a special new type.

Related to https://github.com/dabreegster/ltn/issues/6

[tordans]

Quite a few of those in Berlin are more like a special road type from an osm2streets point of view, IMO. We are still debating how to best represent them in OSM in our OSM Verkehrswende Meetup.

Two examples of modal filters on a straight road segment

• https://www.openstreetmap.org/way/1267121745#map=19/52.47396/13.44290 is mapped by splitting the road to indicate it is still a road for emergency and bike traffic but not cars. Mapillary
• https://www.openstreetmap.org/node/11002284457#map=19/52.47143/13.44984 is mapped just as a bollard might as well be a segment of highway=cycleway to better represent its roads class/meaning. Mapillary

[dabreegster]

I've seen both styles in the UK. https://github.com/a-b-street/abstreet/blob/7c22acb4d811536b877d96c705a52688ba7dc7af/apps/ltn/src/logic/existing.rs#L59 detects short cycleable-but-not-driveable segments that're connected to driveable segments on both sides, and that's worked pretty well so far.

If the filter is more than just a small point along the road, splitting the road is a more detailed way to indicate how much length it takes