[Tagging] Emergency lane used by PSV at rush time

[Eric SIBERT]

> For practical tagging I think it is too theoretical for most mappers to
> understand the difference.
[...]

In somehow, having a not to complicated model or at least a two levels 
model a first simple model could be better.

Back to my initial problem

lanes=2

lanes:condtional = 3 @ traffic_jam
lanes:psv:conditional = 1 @ traffic_jam

Basic data users just need to understand the first key. More advanced 
one may use the two last.

lanes=* wiki would need to be modified to not count temporary lanes. It 
would be more consistent as most of the time only two lanes are available.

Eric