explicitly check for 90 degree turns / turning onto segregated roads

include/extractor/guidance/mergable_road_detector.hpp

@@ -140,6 +140,22 @@ class MergableRoadDetector
     // The detector wants to prevent merges that are connected to `b-e`
     bool IsLinkRoad(const NodeID intersection_node, const MergableRoadData &road) const;
 
+    // The condition suppresses roads merging for intersections like
+    //             .  .
+    //           .      .
+    //       ----        ----
+    //           .      .
+    //             .  .
+    // but will allow roads merging for intersections like
+    //           -------
+    //          /       \ 
+    //      ----         ----
+    //          \       /
+    //           -------
+    bool IsCircularShape(const NodeID intersection_node,
+                         const MergableRoadData &lhs,
+                         const MergableRoadData &rhs) const;
+
     const util::NodeBasedDynamicGraph &node_based_graph;
     const EdgeBasedNodeDataContainer &node_data_container;
     const std::vector<util::Coordinate> &node_coordinates;
@@ -149,6 +165,9 @@ class MergableRoadDetector
     // name detection
     const util::NameTable &name_table;
     const SuffixTable &street_name_suffix_table;
+
+    // limit for detecting circles / parallel roads
+    const static double constexpr distance_to_extract = 150;
 };
 
 } // namespace guidance

include/extractor/guidance/node_based_graph_walker.hpp

@@ -123,7 +123,8 @@ struct SelectStraightmostRoadByNameAndOnlyChoice
 {
     SelectStraightmostRoadByNameAndOnlyChoice(const NameID desired_name_id,
                                               const double initial_bearing,
-                                              const bool requires_entry);
+                                              const bool requires_entry,
+                                              const bool stop_on_ambiguous_turns);
 
     /*
      * !! REQUIRED - Function for the use of TraverseRoad in the graph walker.
@@ -141,6 +142,7 @@ struct SelectStraightmostRoadByNameAndOnlyChoice
     const NameID desired_name_id;
     const double initial_bearing;
     const bool requires_entry;
+    const bool stop_on_ambiguous_turns;
 };
 
 // find the next intersection given a hop limit