[Talk-us] [OSM-talk] Check my junctions - looking for someone to review my plates of spaghetti

Nathan Edgars II neroute2 at gmail.com
Tue Jan 24 04:20:13 GMT 2012

On 1/23/2012 9:52 PM, dies38061 at mypacks.net wrote:
> Over the past couple of months, I have armchair-mapped several highway junctions in the United States which are "commonly complex" in that they involve multiple turn restrictions, street name changes and pedestrian crossing placements.
> I would like to have some critique from someone experienced in mapping such junctions so that I ensure I am following current best practice and am not just creating a bunch of plates of unpalatable spaghetti.
> Two recent junctions are found in the following permalink views
> * http://www.openstreetmap.org/?lat=40.095879&lon=-75.296179&zoom=18&layers=M
> * http://www.openstreetmap.org/?lat=39.128273&lon=-77.237731&zoom=18&layers=M

Yuck. A separate way should not be used for a turn lane (unless that 
lane is separated by barriers or maybe a wide striped-off area).
Corollary: a separated right-turn lane begins and ends approximately 
where the traffic island begins and ends, not where the separate lane 
begins and ends.

Turn restrictions are not for identifying which lane goes where. They 
are for restrictions on turning (e.g. if no left turn is allowed, you 
use a no_left_turn restriction). Thus neither example needs any 
restrictions, since you can turn in any direction from any approach. 
(Some mappers like to use what are, frankly, completely redundant 
restrictions that force you to do what any router will have you do 
anyway, such as no right turn at the intersection if there's an 
island-separated right turn lane.)

The second one is a simple crossing of two divided roads, found all over 
the place (e.g. 
- note if you check against the aerial that the west-to-south right turn 
has recently received an island).

Of course the above is just my opinion, strongly influenced by what I 
have seen as standard practice all over the country.

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