Tony  R
I drove on the B257 coming from South on 2017-07-13 and wanted to turn left onto the marked road towards Kottenborn.
Unfortunately it is forbidden to motortraffic. 

A recent download of the Motoroute_OSM map (GeoFabrik) allowed routing for car/motorcycle.

The road/traffic sign "round white with the red border" (model C 01 in the Netherlands) is placed at it's beginning.

Any 'mapper', thanks for appending this information.