On Wed, 1 Nov 2017 09:03:16 +0100
Michal Fabík <michal.fa...@gmail.com> wrote:

> On Tue, Oct 31, 2017 at 10:29 PM, Warin <61sundow...@gmail.com> wrote:
> > possibly something like 'motor_vehicle:conditional=winter_equipment
> > @ winter'  
> 
> Technically, this looks fine, but is it really necessary to specify
> that winter equipment is required in winter? Besides, I'm not sure
> about the precise meaning of "winter" when using the opening times
> syntax, but in many countries, the restriction applies roughly from
> mid-autumn to mid-spring. If a consumer decides to interpret "winter"
> literally (21st Dec - 20 Mar), it's going to be off by a long margin.

"Winter" is quite useful for situations where the times *aren't*
precise.  For example, roads around here come in three varieties:

1) Those maintained for winter travel.  In the cases I'm aware of,
winter equipment is only legally required when a sign beside the road
says so.

2) Those that are explicitly closed during the winter.  This closure
generally extends from the first deep snowfall to whenever the road
department can schedule a snowplow to go through in the spring.  It's
impossible to give precise dates for this.

3) Those not maintained for winter travel (and generally signed that
way).  It's legal to travel on one of these roads at any time, but a
wheeled vehicle is likely to get stuck, and you won't get a tow-truck
to pull you out until spring, making it a de-facto closure.  Unlike the
explicitly closed roads, these don't get plowed in spring, so the
effective opening date is wildly variable (and varies between vehicles).

A way of expressing "this road is impassible during a vaguely-defined
period of time" is quite useful to cover cases (2) and (3), while
"winter equipment may be required at certain unknown-in-advance times"
would be useful to cover case (1).

-- 
Mark

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