Allow u-turns at merged intersections when the turn lane is explicitly tagged in OSM. This makes the infamous U-turn from Montlake to 520 WB work! The inferred signal timing isn't great, but ah well.

Not regenerating yet

map_model/src/make/turns.rs

@@ -37,11 +37,22 @@ pub fn make_all_turns(map: &Map, i: &Intersection) -> Vec<Turn> {
     if i.merged {
         filtered_turns.retain(|turn| {
             if turn.turn_type == TurnType::UTurn {
+                let src_lane = map.get_l(turn.id.src);
+                // U-turns at divided highways are sometimes legal (and a common movement --
+                // https://www.openstreetmap.org/way/361443212), so let OSM turn:lanes override.
+                if src_lane
+                    .get_lane_level_turn_restrictions(map.get_r(src_lane.parent), false)
+                    .map(|set| !set.contains(&TurnType::UTurn))
+                    .unwrap_or(true)
+                {
                     warn!("Removing u-turn from merged intersection: {}", turn.id);
                     false
                 } else {
                     true
                 }
+            } else {
+                true
+            }
         });
     }