handle non-through case

include/extractor/guidance/constants.hpp

@@ -31,6 +31,11 @@ const double constexpr INCREASES_BY_FOURTY_PERCENT = 1.4;
 
 const int constexpr MAX_SLIPROAD_THRESHOLD = 250;
 
+// Road priorities give an idea of how obvious a turn is. If two priorities differ greatly (e.g.
+// service road over a primary road, the better priority can be seen as obvious due to its road
+// category).
+const double constexpr PRIORITY_DISTINCTION_FACTOR = 2.0;
+
 } // namespace guidance
 } // namespace extractor
 } // namespace osrm

include/extractor/guidance/road_classification.hpp

@@ -15,6 +15,10 @@ namespace extractor
 namespace guidance
 {
 
+// Priorities are used to distinguish between how likely a turn is in comparison to a different
+// road. The priorities here are used to distinguish between obvious turns (e.g. following a primary
+// road next to a residential one is obvious). The decision what is obvious is described in the
+// guidance constants.
 namespace RoadPriorityClass
 {
 typedef std::uint8_t Enum;