[Tagging] Use cases: where would a count of all lanes be useful?

[Stephen Hope]

On 20 September 2011 00:39, Gerhard Hermanns <hermanns at ptt.uni-due.de> wrote:
>
> Traffic simulation (e.g. by cellular automata) is a use case for this. At
> crossroads it can make a huge difference for traffic engineering to know if
> a (turn) lane can contain 3 or 30 vehicles.
> To determine the "capacity" of a turn lane one would need information about
> its length - and one would get this easily if start and end point of the
> lane are known. Otherwise one would have to tag something like
> "turn_lane_left_1=xx" and "turn_lane_left_2=yy" (indicating length or
> capacity or whatever) in case of two turn lanes with different lengths.

I'm not sure I would say "easily".  What you're looking for here is
the number of cars that can be stored in the turning lane without
blocking flow in the through lanes, correct?  Where do you mark the
extra lane width as starting?  Where the lane first splits off? Where
the centre of the lane splits off?  Where the lane is wide enough for
a car to fit?  Where the line markings for a normal lane start?  In
some places, these are all close enough that it wouldn't matter much
for your purposes, but there are places near me where these different
places would make a big difference in car count - 30 - 50m is not
unusual, and some are more.

For a road splitting off from the main road, we would mark the split
in the centre of the road, so for consistency should lane count
changes be done the same way?

Stephen