[talk-au] Roundabouts and routing

[John Henderson]

Roy Wallace wrote:

> +1. A problem with the router requires a simple ROUTER fix. The router
> just needs to be told that when entering a junction with a roundabout,
> that also happens to have an exit, that exit counts as the "first
> exit".

I can just see the people at Garmin falling over themselves to make a 
modification which allows free maps to work better - when they sell 
their own maps and map updates.

I thought long and hard about this issue before I make the first 
"correction" to a local roundabout.  I came to the conclusion that 
roundabout entry and exit points should be separate.  From a safety 
point of view (and probably legal, but I'm no expert there), taking the 
first left turn at a roundabout always involves entering the roundabout, 
travelling on it, and then leaving.

I've found another problem with exit counts at roundabouts which I 
didn't mention.  I feel that Garmin may be responsible for this one. 
It's that highway=service exits are never counted.  I would certainly 
not suggest that we use highway=unclassified as a workaround to this.

It also occurs to me that we might be able to get both these problems 
fixed in one fell swoop, at least for Garmin routable maps.  And that's 
to get the OSM mkgmap program reviewed and modified.

Or am I being over-optimistic?

John