[OSM-talk] traffic signals at dual-carriageway and complicated intersections

[Simon Hewison]

Brent Easton wrote:
> I think it has been mentioned before, but I think the only real answer is that the middle square of the intersection becomes it's own way with a 'junction=traffic_lights' tag. 
> 
> The renderers can than display just one symbol at the c.o.g. of the junction way. This reflects the reality that there is only one junction with one 'set' of lights, not 4 seperate junctions, each with their own set of lights.
> 
> This also works where a divided road is crossed by a single way, the short line connecting the two ways would be created as it's own way with 'junction=traffic_signals'.


Nice idea. This also highlights the point that renderers and navigation 
systems need the ability to de-clutter their incredibly detailed maps for the 
benefit of the end user.

For instance, given a typical roundabout with a two-way street approach, you 
wouldn't have driving instructions saying

Drive North along the A4180 for 2km
Bear right on the A4180 for 50 metres (one-way road)
Join the "Polish War Memorial" Roundabout, and drive clockwise around the 
roundabout for 15 metres.
Continue to drive clockwise around the "Polish War Memorial" roundabout for 15 
metres.
Continue to drive clockwise around the "Polish War Memorial" roundabout for 7 
metres. (you can't exit here, it's a one-way road going the other way)
Continue to drive clockwise around the "Polish War Memorial" roundabout for 7 
metres.
Turn right onto the primary_link road (one-way) for 170 metres.
Merge onto the A40 (one-way road, trunk road)

For written or spoken directions it would be

 From the A4180, drive for 2km
Take the third exit onto the A40 trunk road, eastbound at the Polish War 
Memorial roundabout.

Likewise, for printed maps, unless you're really zoomed in, you don't need to 
know that each link road is one-way, or that there may be traffic signals on 
each entrance to the roundabout.

-- 
Simon Hewison