This is a problem that may not have a solution.

It always occurs when trying to route to or from a road of GeoRoadType geoRoadInterstate. These are described in the documentation as limited-access highways.

I suppose this is essentially correct behaviour since you cannot actually join a motorway, or the US equivalent, except at junctions.

However there doesn't seem to be any way to determine a roads GeoRoadType in advance and so program accordingly.

If anyone knows of a solution I would be very interested.

Roger