[OSM-newbies] Intersection tagging redux

[Randy]

James Ewen wrote:

>Okay, I'm still pondering how to tag this intersection properly. The
>road network data has been imported from GeoBase, but I feel that the
>ways depicting the intersection are not accurate.
>
>The main N/S roadway is a dual carriageway, two lanes each, with
>decelleration/accelleration lanes added on the right on either side of
>the intersection. There is also a left turn lane added, making the
>roadway 4 lanes wide at the intersection. The right hand lanes have
>islands, so they should get a separate way around the corner in my
>mind. The left hand turn lanes are not separate so I would choose to
>not show them as a different way.
>
>The E/W roadways have decorative planters separating the ways as they
>approach the intersection, with a single lane each way. However
>through traffic is not allowed straight across the intersection. This
>restriction is enforced by concrete islands that direct traffic flow.
>
>The GeoBase depiction shows the N/S left turn lanes as separate ways.
>The forced left turn lanes on the E/W roadway are depicted as well,
>but these 4 turn lanes share 4 common nodes, creating a diamond in the
>middle of the intersection.
>
>Would a routing engine possibly mistake these common nodes as a valid
>routing choice, and try to get people to follow the routing in an
>obviously incorrect manner? Should these ways cross each other without
>common nodes? By not having a common node, there would be no way for a
>routing engine to make a mistake. These ways do indeed all cross at
>the exact same physical level on the pavement, with no grade
>separation, but it is not legal to change from one way to another at
>that point.
>
>
>Here's the current OSM depiction.
>http://www.openstreetmap.org/?lat=53.53393&lon=-113.26316&zoom=20
>
>Here's a satellite view from Google just for visualization.
>http://tinyurl.com/yjmo6o2
>
>Here's a Google Streetview of the intersection.
>http://tinyurl.com/y9b7qa2
>
>(gotta love Streetview! Just got it for our area within the last week,
>hence the redux)
>
>BTW, GoogleMaps doesn't show the turn restrictions either... I want
>OSM to show it properly.
>
>James
>VE6SRV

Hi James,

Here's what I would do. (It's probably all wrong, but I just did one with 
similar rules, but not quite as extensive an island system.) (PS., I asked 
for comments, too, but got none.)

I tried something similar to what you did, but decided it was just too big 
a mess. Yes, I'd connect all the nodes, but I'd simplify the ways some.

I'd ignore the island in the center, and make a single way connecting the 
two divided highway lanes and the side (E/W) streets.

I'd then use turn restrictions, no_straight_on, on both sides of the E/W 
street with "from" being the street, "to" being the same street on the 
opposite side, and "via" being the connector between the two divided 
highway lanes (I'm not sure whether you should also include the two nodes 
as vias, I suspect it doesn't matter).

I'd remove the left turn lanes, and show the acceleration/deceleration 
lane as you have, i.e., the diagonal turning lanes , but not the parallel 
lanes . And, I'd make sure the oneways were all there where appropriate 
(which you have), but not on the connector way, of course. I think that's 
the best compromise unless you want to micromap it. If it is in fact 
illegal to turn right directly into the E/W street if you miss the turn 
lane, then you might want a no_right_turn restriction on that small 
segment approaching the cross-connecting segment.

Hopefully that makes sense, and also hopefully, someone will have a better 
suggestion (that I can carry over to my own situation).

Randy

-- 
Randy