[OSM-talk] Lane turn restrictions

[Steve Hill]

On Wed, 19 Aug 2009, Yann Coupin wrote:

> I once started a proposition to do just that but it didn't get much traction, 
> feel free to discuss it.
>
> http://wiki.openstreetmap.org/wiki/Proposed_features/Relation:type%3Droute_instruction

I've not read the discussion page yet, but some initial thoughts:

Your first examples aren't topologically identical - the first is a 2 lane 
road with a short 3 lane section followed by a right hand turn whilst the 
second is a 3 lane road with a right hand turn immediately followed by 
dropping down to 2 lanes.  Of course, this doesn't give you enough detail 
to know what lane you've got to be in (although you could make some 
educated guesses).

I also don't see the need for phonetics to be tagged (in fact, it seems 
harmful because it breaks multi-language support).  We don't know what 
kind of display device is going to be used (whether it be on-screen 
instructions, text to speech, etc.) and it should be up to the software to 
decide how to present it to the user rather than being explicitly tagged 
like that.

Overall, the proposal seems a bit too complex - I had envisaged a 
simpler system whereby you could set a relation similar to a turn 
restriction, such as:
  	TAGs:
 		type: lane_restriction
 		lanes: 1,2
 	Members:
 		from: <way the user is driving along>
 		to: <way the user wants to turn onto>
 		via: <junction node>
Whereby that marks a restriction that lanes 1 and 2 (the left two lanes, 
in the case of the UK) cannot be used in a route using the <from>, <to> 
and <via> members.

It would actually be nicer to be able to tag which lanes are allowed 
rather than which are disallowed, but that would be inconsistent with the 
existing turn restrictions (maybe that isn't a problem?  comments?)

-- 

  - Steve
    xmpp:steve at nexusuk.org   sip:steve at nexusuk.org   http://www.nexusuk.org/

      Servatis a periculum, servatis a maleficum - Whisper, Evanescence