U-routes
U-routes (Uitwijkroutes) are permanent routes that are used to reroute traffic in case of a closure of the main road.
The route identification can be added as alternative name to the street name.
The road type should be at least Minor Highway.
The U-routes are marked with an "U" plus number, like U27.
More information on U-routes can be found in the Dutch Wegenwiki.