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From Wazeopedia

Routing server

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Pruning: wordsmithery
== Client-based routing ==
Calculating an optimal route is a difficult task. While the client device app has a routing algorithm included, this is not used unless there is no connection to the Waze server. Client-based routing only uses cached map tiles. It does not use real-time traffic data , reports or reportsclosures, because this information is not accessible. Therefore, and it does not provide an estimated ETA.
== Routing requests ==
* Whether to allow or avoid [[toll roads]]
* Which, if any, [[Carpool, HOV, Transit lanes|toll and HOV]] passes to apply (some segments are permitted only to those who hold the proper pass)
* Whether to avoid [[ferries]]{{Ferry|Ferries}}
* Whether to avoid {{Freeway|Freeways}}
* Whether to allow, never allow, or avoid long unpaved roads
* Whether to avoid avoid [[Difficult turn|difficult intersections]] (turns marked "difficult" through nodes or junction boxes).
* Vehicle type
** {{Passageway}} has a type-specific [[Routing penalty|penalty]].
** [[Partial restrictions|Segment restrictions]] allow or prevent travel by certain vehicle types.
 
== Different route lengths ==
 
=== Pruning ===
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. At distances farther than a certain threshold value from the origin or destination of a route, roads lower than a certain type tend not to be considered. Pruning thresholds with confidential, variable, increasing values exist for {{Street}}, {{Primary Street}} and {{Minor Highway}}, respectively. There is evidence that {{Major Highway}} is never pruned. {{Freeway}} and {{Ramp}} are 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 ===
Generation of routes longer than 1000 miles in Waze used to be impossible, but in 2018 a new mechanism for extra-long (XL) routes was put into place. This pieces together multiple long routes to generate one extra-long route. To save time and avoid routing timeouts, instructions and geometry details are omitted in the middle of the route during initial calculation, but they are produced and listed later as the user drives along the route. Dependent upon multiple factors such as server load and road types, transcontinental routes can be calculated in Waze with this mechanism. It is also evident that, since XL routes are combinations of shorter routes, the aforementioned pruning behaves differently for them, so that lower road types may appear in the middle of extra-long routes.
== Real-time current road speeds ==
The routing server uses real-time road speeds (from recent Waze app users if available) and combines the average, historical speed of the segment broken down into 10-15 minute chunks. The time to pass through a segment is tracked separately for each route out of a segment. For example if a segment ends with only a left and right turn, then the routing engine isolates the time through the segment to turn left and the time through the segment to turn right. This detailed speed information is proprietary and is not displayed in the Waze Map Editor.
It is known that Waze prefers to use real-time reports of current road speeds over historical average road speeds. Waze also uses traffic congestion reports to reroute around slow traffic. <!-- Early versions of the client would also report when traffic speeds were good - this was removed due to map clutter. But Waze will still be receiving this information. -->The speeds of recent Wazers traveling on a road will be factored into the route given to subsequent Wazers traveling on the same road.
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.
 
== 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. This might 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. Another reason for a route to change could involve which road types are used. This is explained in the next section.
 
== Changes in routes due to different route lengths ==
 
=== Pruning ===
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 ===
Generation of routes longer than 1000 miles in Waze used to be impossible, but in 2018 a new mechanism for extra-long (XL) routes was put into place. This pieces together multiple long routes to generate one extra-long route. To save time and avoid routing timeouts, instructions and geometry details are omitted in the middle of the route during initial calculation, but they are produced and listed later as the user drives along the route. Dependent upon multiple factors such as server load and road types, transcontinental routes can be calculated in Waze with this mechanism.
== Average road speeds ==
If the average or historical road speed is not correct, then the route will may not be optimal. However, it is never recommended to delete deletion of segments in order to reset the average road speed for that segmentis not recommended. Waze uses the data from Wazers traveling through the segments to update the average speed, and oftentimes an anomalous historical road speed is automatically corrected with further data collection. If you suspect Waze is not using appears to disfavor the use of certain segments along a route, there are a number of other reasons that can cause such a situation. Don't assume deleting the segment is the place to start. The following are reasons why the routing engine might not use the average road speed.
=== Time-of-day variations ===
Consider a road that most Wazers drive at 5 PM when the average speed is 12 MPH. At 10 AM when the road is clear and the average speed is 60 MPH, it is the best road to take. If Waze only has historical speed data from 5 PM, it will assume that the speed of the road is 12 MPH all day, and it may not recommend You can, of course, this road. As more people drive this road closer to the road yourselftime of day when a given route is requested, and Waze eventually learns the speed will get a better guess for that time. We do not know how long Waze holds the older data in computing the average speed. However, if Waze does discard old at that time information, you might not accumulate new time faster than it is discarded. It is also possible that your times are being ignored as being abnormal.
=== Shrinking window ===
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