The Waze routing server uses a system that penalizes routes to avoid undesirable situations. Penalties are measured in extra time added to the route, on top of the calculated time that driving the route is expected to take based on historical and real-time traffic data. This extra penalty time does not affect the estimated time of arrival, so it is invisible. When multiple routes are compared, however, the penalized route may not be offered even if it is the fastest route, because the invisible extra time makes it look like it takes longer than a non-penalized slower route.
Background
Historically, Waze routing was 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 were applied as a routing penalty. For example, a soft restricted turn indicated by a red turn restriction arrow and a purple questions mark does not prohibit the turn, but rather it applies a high penalty to any route through the turn. Since this is the default state of any newly connected road, this penalty permits routing through new roads where no one has driven or edited them to give better data, where no nearby options exist with allowed turns. Hard restricted turns had an even higher penalty in the past, but as the map matured through editing, the Waze team decided to make hard restricted turns an absolute prohibition on routing.
Penalties have been used for other segment properties beyond restrictions, and it has also been used for certain road configurations. The list of penalized segment properties has grown with advances in user-configurable navigation settings. Penalized road configurations have been developed to provide a smarter routing experience for the growing user base.
Segment properties
The following segment properties cause routing penalties:
Soft allowed turns (green arrow with a purple question mark)
Toll roads for clients with avoid toll roads selected in the app
Unpaved roads for users with "don't allow unpaved roads" 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.
Passageways for all vehicle types except motorcycle
Freeways for users with "avoid freeways" selected in the app
Difficult turns for users with "don't allow difficult turns" or "always reduce difficult intersections" selected in the app
Road configurations
Other routing penalties are based on road configurations.
U-turn
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.
Detour
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.
Preventing routes with certainty
The following conditions prevent routing and do not involve penalties:
Closure
Hard turn restriction
Time-based turn restriction (depending on whether conditions are met)
Time-based segment restriction (depending on whether conditions are met)
Non-drivable road types
Wrong way of a one-way road
Disconnection of one road from another
Deletion of a road
In the past, many of these conditions created penalties and could not prevent routing with certainty, so disconnection and deletion were necessary. This table explains the various uses and trade-offs of routing prevention methods.
