Detour Prevention Mechanisms
Waze routing includes a mechanism to prevent routing off a highway/freeway only to be routed right back on the same highway/freeway. The assumption is that drivers will prefer to remain on the highway/freeway even if waze calculates that taking a series of ramps or other collector/distributor roads is slightly faster or shorter.
Waze routing will reduce the chances of a detour off a highway/freeway and back on that same highway/freeway when all of the following conditions are met:
- the last segment on the highway/freeway before the detour has the same street name and same city name as the next highway/freeway segment after the detour (the segments are considered to have the same name if either the primary name or alternate names are the same; unnamed segments are not considered as having the same name),
- the detour is more than one segment long, and
- the detour is under the threshold length as defined below.
It is important to understand that Waze uses a penalty-based routing system. It computes the total penalties for a route and selects the one with the least cumulative penalty. Therefore it is possible for big detour routes to occur when the primary route is extremely slow.
- For divided roadways that have the same name on both carriageways, the big detour prevention mechanism will prevent U-turns that traverse more than one segment. Thus in the intersection below, the configuration on the left will be used to route a U-turn because it uses a single segment between the two parallel roadways with the same name. In contrast, the configuration on the right will not use the U-Turn road because it branches from another segment causing multiple segments between the two parallel roads with the same name.
- Be careful where route number concurrencies begin and end as the big detour mechanism may be triggered by discontinuity of alternate names. Where an alternate route exits a freeway or highway over ramps at an interchange, if the ramps do not have the same alternate name as the segments entering and leaving the interchange, the big detour prevention mechanism may prevent routes over the ramps.
Waze has a small detour prevention mechanism to deal with instances where Waze calculates that that its a few seconds faster to continue straight or make a right at an intersection and make a u-turn rather than just turning left. Waze will eliminate such detours if there is under a one minute difference in the routes.