[Tagging] barrier enforcing maxwidth

[Lauri Kytömaa]

Colin Smale wrote:
> Regarding maxwidth:physical, the examples in the wiki are actually from
> Finland where they apparently have explicit signs for the physical width.

Just for clarification: even here in Finland the signs are rare, and
the only two
examples I remember straight away on public roads are on reasonably
remote low traffic highways where the carriageway width is otherwise maybe
6 meters (just enough for a lorry and a passenger car to pass each other at
speed and passing places at regular intervals), but at a single point a bridge
is narrower, but wide enough for two oncoming passenger cars to cross the
bridge at the same time. They don't need a sign giving the other direction
priority over the the other, but drivers need to realize they might have to slow
down or even stop if there's oncoming traffic. A fellow mapper here recalled
seeing them on some garage entrances, too.

The signs for physical width might possibly have, just as the signs of
physical free height do have, a number that's rounded down to nearest
10 cm minus 0,1 meters. For height signs that's the supposed margin of
error (to allow for changes in height due to repaving, for some snow on the
ground and on the vehicles, and to leave some air space anyway).

It's probably illegal to ram your vehicle into a too narrow gap on
public roads, even if there are no signs telling the available width. In a
sense maxwidth:legal= (when in addition to maxwidth), when they're
the same, tells the parser that the width is "just" a signposted legal
limit, if a physical maximum isn't present.

Even if the signs usually tell most of the facts, osm data shouldn't be
only about the signs.

-- 
alv