From Wazeopedia

Routing server

981 bytes removed, 5 months ago
took out fastest routing section due to dated info and redundancy. also took out the caching thing from the different origin section
== Routing requests ==
When a user requests a route calculationwith a network connection, the request is sent to the Waze server. That route is then transmitted back to the client device and displayed.
The requests for routing vary according to the settings chosen for the user's account on the client device. Under Navigation one can choose:
Since Waze uses the future expected time of arrival onto a road segment in order to calculate the expected speed on that segment, it cannot use real-time data too far in the future. So longer trips (on the order of 30 minutes or more) will include future time slots where current traffic data is not available when initially calculated. As the trip progresses, any real-time traffic data that is available causes the client to recalculate the route and the ETA.
== Fastest routing ==
Waze knows the average speed of every confirmed road between you and your destination. The Waze server can calculate which list of roads to take to minimize the total travel time.
While every request is processed in real-time, by observation it appears that Waze [[glossary|caches]] some requested routes or major points. This means if it already knows the best route from B to C, and you ask for a route from A to C, it might just calculate the best route from A to B, once it checks that there isn't a better route bypassing B altogether. This does mean that when there is a [[Timeline of updating process|Live map update]] some routes might be less than optimal for up to a day as routes are cached and recalculated.
While a complex calculation, calculating the optimal route is possible. The complexity arises over the "average speed" of the roads.
== Changes in route due to different origin ==
Consider calculating a route from A to Z. The suggested route might be A to B to C to D to Z. Then calculate the route from B to Z. You might get a suggested route of B to C to E to Z. At first glance, this suggests one route is not optimal because the [[Glossary|origin]] changed. We can guess at what might be happening. There might be a problem associated with the possible caching of routes. Or there This might be have resulted from a "timing window" effect. The different arrival time at C might change the best route to Z. Or there might be a fine tuning effect in the route, perhaps to avoid too many turns. So by dropping the segment A to B, the segments C to E to Z no longer exceed some threshold. This effect can be observed while driving. If you recalculate a route to a destination while driving along an already calculated route to that same destination, the route can change.
Waze sometimes offers This effect can be observed while driving. If you recalculate a new route to bypass heavy traffic a destination while driving along an already calculated route to that same destination, the route can change. Another reason for a route to change could involve which raises road types are used. This is explained in the question as to when and how Waze considers reroutingnext section.
== Changes in routes due to different route lengths ==
=== Pruning ===
In addition, it It is known that the Waze routing engine can't calculate every possible route for long-distance routes, so it takes shortcuts by removing lower road types from consideration in the middle of longer routes. This effect is commonly called '''route pruning''' and can potentially result in the route changing dramatically when lengthened slightly. For example, according to Waze support ({{as of|July 2011|lc=y}}), the section of a route more than 10 km from each endpoint is heavily weighted toward road types above {{Street}} (i.e. Primary Street or the various Highway types). Longer pruning thresholds exist for {{Primary Street}} and {{Minor Highway}}. It is believed that {{Major Highway}}, like {{Freeway}} and {{Ramp}}, is never pruned. The pruning mechanism uniquely accounts for [[Creating and editing road segments#Special properties|routing road type]], so a Primary Street with routing road type +1 would be pruned at the same threshold as a Minor Highway.
=== XL routes ===