[Tagging] Divided highways, and not so divided highways, one way or two

[Markus]

On Thu, 10 Oct 2019 at 16:10, Snusmumriken
<snusmumriken.mapper at runbox.com> wrote:
>
> For example if you try to create a routing advice for a car journey.
> Let's say that the journey starts at Main street number 10 and that
> Main street is a two way street where the two directions are legally
> separated. Let's say that number 10 is on the right-hand side of the
> road and we are in a country that drives on the right side. Let's
> further say that the shortest way to the destination would be to cross
> the legal separation and take left. But that would be illegal. But
> there is no way the routing engine could know that. Unless the two
> directions are separated.

That's not true. There's another way to tell routers that it is
illegal to change lanes: by adding that information to the highway=*
way. There's already a tag for this: change:langes [1] (> 90 000
uses).

While mapping separate ways where there is no physical barrier works
for car routing, it breaks pedestrian routing and there's likely no
way to fix this. Pedestrians usually are allowed to cross a painted
line that cars aren't allowed to cross (at least in Europe).
Therefore, if the road in your example is mapped with two separate
ways, a routing engine would make pedestrians do a detour (possibly a
long detour), even though they could just cross the street.

[1]: https://wiki.openstreetmap.org/wiki/Proposed_features/change

Regards
Markus