I feel it's only fair to mention that some of these no_u_turn restrictions are flagged as invalid by JOSM but that is because it (wrongly in my opinion) seems to take the direction of the via way into account.
Our implementation of turn restrictions does not handle via ways, only via points.
Can I make this a feature request then? :) Consider the following A B C --------+-------> | <-------+-------- D E| F | \/ G ABC is oneway in direction ABC FED is oneway in direction FED BE is twoway but is marked with direction BE U turns are not allowed for FEBC nor are they allowed for ABED I have several of these near me and I'm sure they're fairly common (if not yet in the OSM database). Current mkgmap maps will tell me to make a U turn (FEBC or ABED) Cheers Paul