[OSM-talk] Turn left restriction on two way highways

John F. Eldredge john at jfeldredge.com
Wed Dec 29 18:31:31 GMT 2010


It makes sense to me to use a left_turn_allowed tag, so as to map the exceptions.  In the USA, left turns are allowed unless signed otherwise, so a no_left_turn tag is mapping the exception.

-------Original Email-------
Subject :Re: [OSM-talk] Turn left restriction on two way highways
From  :mailto:Alan_Mintz+OSM at Earthlink.Net
Date  :Wed Dec 29 11:16:22 America/Chicago 2010


At 2010-12-29 08:19, Diego Woitasen wrote:
>  In Argentina we have a general rule. If you are driving in a two way
>highway (residential, primary, secondary, etc) you can't turn left.
>You can do it only if there is a sign and/or traffic light with the
>turn left row. We are discussing in the Argentina forum about if it's
>make sense to map the no_turn_left restriction on every crossing road
>or not. I think that we should drive the exception to the rule, the
>routing software should apply the default restriction.

You should map the exceptions (where left-turn IS allowed).

Don't know what to call them instead of no_left_turn. Maybe left_turn or 
left_turn_allowed.

In states in the US where U-turns are allowed unless specifically 
prohibited by a sign, we map only no_u_turn where it is prohibited, not all 
the places where it is allowed.

There was some discussion in the past about creating defaults for various 
rules such as these turning rules, speed limits, etc. tagged on 
administrative boundaries (country, state, county, etc.), for use by 
routing software.

--
Alan Mintz <Alan_Mintz+OSM at Earthlink.net>


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John F. Eldredge -- john at jfeldredge.com
"Reserve your right to think, for even to think wrongly is better than not to think at all." -- Hypatia of Alexandria


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