[Voting] Feature Proposal - Deprecate crossing=zebra in favor of crossing:markings

[Minh_Nguyen (Minh Nguyễn)]

@Nadjita

An example, why the “let’s tag it explicitly” approach can be problematic, is shared bike/pedestrian ways in Germany. We tag them with highway=path + foot=designated + bicycle=designated + segregates=yes/no. But that would also allow horse riding on these paths, yet no one adds horse=no, or cared about small_electric_vehicle=*. So in order to “know” that horses are forbidden on these roads, and small electric vehicles are allowed, the router would have to start guessing which situation is tagged, instead of blindly following these tags.

Just to be clear, I’m not suggesting that these two approaches are mutually exclusive. crossing_ref=zebra seems to be the most informative tag for a zebra crossing in the UK, but other secondary keys can serve as a backstop for less sophisticated data consumers. To me, there’s little harm in allowing these other keys to be used in combination on a best-effort basis.

Maybe it seems obvious to us that a zebra crossing in the UK would be marked with zebra stripes, but inevitably there will be a long tail of obscure designations as well. For example, in Utah, a zebra crosswalk consists solely of zebra stripes – no Belisha beacon. But the stripes alone denote whether the motorist must wait for the pedestrian to clear the street.

We don’t have an established tag for these rules, and we can’t expect any armchair mapper to know them. Compare this to markings or signalization, which a mapper can easily observe and which data consumers already consume – this is what I mean by a basic characteristic. A (still hypothetical) data consumer that needs to know the specific traffic rules at each crossing may have to implement some heuristics based on crossing:markings=zebra or, if they’re lucky, crossing_ref=US:UT:zebra. You may be shocked at this “guessing”, but such informed guesses are the bread and butter of any OSM data consumer.

@Nadjita

Another problem would be if the legislation for zebra crossing changed. Let’s consider a country that explicitly forbade riding your bike on a zebra crossing to get to the other side, now starting to allow bicycles. If they were tagged with crossing_ref=zebra, the only thing that needed to change was the documented “template” value of bicycle=no to bicycle=yes, and not millions of crossings.

This is an argument against tagging nitty-gritty details that we’ve inferred. I agree that we probably shouldn’t tag crossing:restriction=no_jaywalking_nearby on a UK zebra crossing, as suggested tongue in cheek in the UK thread. That detail is merely an inference on our part. The rule is written on paper and can change on paper. But even if the authors of the TSRGD or Highway Code decide tomorrow that zebra crossings shall be rainbow-colored, they cannot magically cause rainbow paint to be splattered upon all the country’s zebras overnight.

Access restrictions in some countries are more like rules on paper, depending on things like zebra stripes rather than explicit signs. Unfortunately, the concept of default access restrictions for routing has been mostly in the realm of wishful thinking for the better part of this project’s history. But I don’t think the UK has completely avoided tagging access restrictions just because they can technically be inferred from other tags.