Hi Marko,
Anyway, the problem is that the U-turn restriction is ABCD (A=from,B=via,C=via,D=to) while BCD (B=from,C=via,D=to) would suffice.
BCD restriction would be interpreted as turn-left restriction for cars coming from other road, which in most cases would be wrong. There is no shortcut for 4-points U-turn restriction. I'm not sure, what are recommendation in OSM, but I think cgpsmapper is logical in its definition of restriction. Restriction should consist of nodes and ways between these nodes. There should be no guessing how to get from a node to next one. OSM relation can include only a part of these data, for example 2 nodes and a way or 4 nodes. Any combination should be interpreted, converted to standard definition and used if can be stored in Garmin format. -- Best regards, Andrzej