[OSM-talk] Highway=trunk : harmonization between countries ?

[Richard]

On Tue, Aug 22, 2017 at 08:09:25PM -0400, Greg Troxel wrote:
> 
> john whelan <jwhelan0112 at gmail.com> writes:
> 

> > As someone who lives in a city street with one school in the middle and one
> > at either end posted at 40 km/h with an average traffic speed of 60 km/h
> > and over 100 km/h from some high school kids driving to and from school I
> > would prefer it if traffic stuck to the posted speed limits.  Cars running
> > across front lawns to avoid collisions are not unknown.
> 
> That sounds crazy, but I would guess that it isn't the people actually
> paying attention going 48 that are the real issue!  But in all
> seriousness, that sounds like an actual problem, not an OSM
> representation problem.

it would become an OSM problem if someone decides to tag this road 
with maxspeed:practical=60. A router may then decide to route you 
to this route instead of some alternative that would be much faster 
for people who decide to respect speed limits at schools.

In cities I believe that maxspeed:practical can be usefull foremost
in situations where traffic flow is for whichever reason much slower 
than could be expected for an average city road tagged identically.
That is because on average other factors like traffic lights, left
turns, yielding etc determine the travelling speed much more then
driving speed. None of those OSM and OsmAnd is particularly good at..

Also consider the effect of the majority and other statistical effects. 
If in Montana or wherever it is common to drive 20-40 miles faster 
than posted on most rural roads than the router will probably do correct 
routing decissions on average even without maxspeed:practical. 
Tagging some roads with maxspeed:practical would have only the 
effect to distort routing decissions. You would have to tag the 
large majority of roads with this tag to achieve a similar effect 
like not having it on any of those roads.

Richard