On 1/23/2012 9:52 PM, dies38...@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.
http://www.openstreetmap.org/?lat=28.38582&lon=-81.506134&zoom=18&layers=M
- 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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