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The Waze routing servers use a system that associates restricted turns and directions as a penalty amount. When it then compares the different routes, it looks at the cumulative penalty points and the lowest amount of penalty points is the better route.
Background
Waze routing is intended to work in two very different environments at the same time. One uses map information that has been carefully corrected by a group of dedicated editors. The other uses map information that was imported from an external database with no editor corrections. To support both systems the Waze development team decided to use a penalty-based routing system. That means the various segment and junction node properties that restrict certain directions between segments are applied as a routing penalty. For example, a turn restriction indicated by the red turn restriction arrow does not prohibit the turn, rather the turn restriction applies a high penalty to any route through the turn. This penalty-based routing system permits routing to a point on street where all turns onto the street are incorrectly set as restricted. This provides for some routing in areas that have not been edited carefully or correctly.
Segment properties
The following segment properties cause routing penalties:
Non-drivable road types including Walking Trail, Pedestrian Boardwalk, Stairway, Railroad and Runway/Taxiway.
Toll roads for clients with avoid toll roads selected in the app.
Dirt road/4x4 Trail for clients with "don't allow" selected in the app, or when segment length exceeds 300m with "avoid long ones" selected.
Parking lot roads and private roads when transitioning from one of these two road types to a different road type. Not when entering these two road types. This is discussed in detail in Private Installations.
Road configurations
Other routing penalties are based on road configurations.
Segment too short to allow two left turns Waze will penalize a route (which forms a U-turn) with two left turns in less than 52.49 ft (16 m) in right-hand traffic jurisdictions or with two right turns in less than 52.49 ft (16 m) in left-hand traffic jurisdictions. The specific details on configuration, and criteria for this penalty are documented in the Intersections page of the Junction Style Guide.
Ramps should prevent detour Waze penalizes some routes that leave a highway or freeway only to immediately return to the same freeway or highway. This is covered in more detail in Detour Prevention Mechanisms.
When a new node is created along a current or new segment, the node will default to a 5 second penalty through that node until someone drives across it and the map tiles are rebuilt with the new data. After that point the 5 second penalty is removed and the measured transit time through that node is used.
Preventing routes with certainty
If a segment should never be used for routing, it should not be connected to the road network. For example, Waze may route over walking trail or stairway segments connected to the road network if conditions are such that the penalized route is still found to be the best route. This is common where there are no alternate routes, such as when Waze finds that the origin or destination is on the penalized segment.
