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Routing server

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When using the Waze application, Waze servers use routing algorithms to determine the best path for a given route at that particular time. The specific details of the routing algorithms used by the Waze server are not publicly disclosed; the following is based on observation, speculation, and some information revealed by Waze staff. Tthe The operation of the routing server is considered to be proprietary and a competitive advantage to Waze. The information on this page is subject to change, and any information that has been revealed may be incomplete or out of date.
== 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 or reports, because this information is not accessible, and it does not provide an estimated ETA.
** {{Passageway}} has a type-specific [[Routing penalty|penalty]].
** [[Partial restrictions|Segment restrictions]] allow or prevent travel by certain vehicle types.
 
== Missing roads and incorrect junction connections ==
Waze tries to find the best route based on the above navigation settings. Obviously it can only route based on roads that it knows about, so a given route will not be optimal if a better route does not have all the roads with correct connections and allowed turns in the [[Waze Map Editor]]. Also if [[Segment length|segments are less than {{:Segment length/Minimum}}]] they can cause routing issues.
== Real-time current road speeds ==
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.
== Problems with average Average road speeds ==
If the average road speed is not correct, then the route will not be optimal. However, it is never recommended to delete segments in order to reset the average road speed for that segment. Waze uses the data from Wazers traveling through the segments to update the average speed. If you suspect Waze is not using 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 5pm 5 PM when the average speed is 12 mphMPH. You choose your route at 10am At 10 AM when the road is clear and the average speed is 60mph. It 60 MPH, it is the best road to take. If Waze only has historical speed data from 5 PM, but Waze chooses a different route because it has no information about will assume that the speed at 10am and assumes of the speed road is 12mph 12 MPH all day., and it may not recommend
You can, of course, drive the road yourself, and Waze eventually learns the speed 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 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.
More === Shrinking window ===If there are enough recorded speeds on a road, then Waze users would uses a shrinking window of speeds to better estimate the average speed at the current time. Waze uses the speed of each road segment (in both directions) in intervals as small as 30 minutes. So a two-way road might have up to 96 average road speeds in a day. It can be assumed that when there are insufficient records for an individual time slot, a wider time range is used (up to a full day). As the road is driven more at different times, the time slot shrinks. Additional information is used based on the day of the week. There is no evidence that Waze records speeds for larger date ranges such as months or seasons; however, it will update its average speeds relatively quickly when seasonal traffic patterns change. Waze uses the average road segment speed for the time slot that applies at the time when a user is expected to arrive at that road segment. Because of this time window, Waze suggests different routes at different times of day. This is dependent on how many times are recorded on the roads along the route. If they're all recorded at about the same time of day, then the time window does not help fix this. If 1,000 times are recorded at about 5 PM and 2 times are recorded at 10 AM, then the 10 AM average speed still is based mostly on times from around 5 PM.
=== Turn delays ===
On a segment of a road, your a user's average speed can be very different depending on what you do is done at the end of the segment. Traffic going straight through a traffic light might go very fast while traffic turning left might wait a very long time. A freeway exit lane might go fast while traffic continuing hits congestion.
[[Image:SegmentTraffic1.png|right|350px]]Waze has the ability to separately track the average speed of traffic that passes through a segment, but exits to different segments. The routing engine takes this into account. In the diagram, multiple times are tracked for traffic flowing through Seg4 based on the segments to which it exits. There are then two average drive times for:
For this reason it is important to keep long segment lengths before junctions as traffic congestion at the junction might affect exits differently.
To understand this problem better, consider if we add a short Seg8 between Seg7 and Jnct4. Let's say the traffic exiting Seg10 backs up all the way to Seg7 (easy enough, since Seg8 is short). Because Seg7 only has a single exiting segment (Seg8), the routing server is only able to collect a single average speed — it can no longer distinguish traffic by where it is going ''after'' Seg8. Now the through traffic going to Seg9 appears to Waze to slow down through Seg7, even though it doesn't in reality. At a minimum this causes an incorrect ETA for routing, and it might actually cause traffic to be rerouted unnecessarily, and less optimally, through another route. Hence, if there is a chance that traffic can go in different directions at a junction and that junction can experience different amounts of congestion, you should keep the segment before that the junction should be kept long, or a [[junction box]] may be used.
Note this === Outdated and abnormal road speeds ===Average speeds can change over time, and recorded times can be abnormal or wrong—and can stay wrong for a very long time. This may be due to users recording inaccurate speed data by doing things like walking, biking or sitting in their driveways with Waze open. Also, if [[Segment length|segments are less than {{:Segment length/Minimum}}]] they may not be long enough to record accurate transition times. There is some evidence that abnormal road speeds and old road speeds are discarded, or at least not presented to users through used in calculating the average speeds of roads. == Recalculation ==When Waze Map Editorreceives notification of traffic conditions, but it uses the actual speed of roads on your route, rather than the average speed. This is based on [[Real time closures|real-time closures]] and automatic traffic condition reports - light, moderate, heavy traffic or complete standstill. Manual reports of traffic jams and accidents are for display only visible and do not change routing. ETA is updated in response to a user's progress on the routing serverroute and in response to these real-time traffic conditions. If real-time traffic conditions make the given route significantly worse than alternatives, Waze may provide an automatic recalculation. The benefits of this are balanced against the perceived hassle of changing one's route.
== Traffic lights and stop signs ==
Waze does not record the location of traffic lights. While some GPS navigation offers guidance like "turn right at the next traffic light" the information is frequently incomplete, incorrect or outdated. The consensus view is that Waze should not record the location of traffic lights.
Waze does take traffic lights and stop signs into account by noting the effect they have on traffic speed. Consider a traffic light with long waiting times. The road segment leading to that traffic light will have a low average speed. If the average speed (based on the average waiting time) becomes low enough, a longer route that avoids the light becomes the preferred route. This has been observed in practice and is an example of ''emergent behaviourbehavior''. Waze isn't programmed to avoid traffic lights but it does avoid slow roads; if the traffic lights make the road slow then Waze avoids them.
Some drivers regularly take longer routes — even winding through side streets — to avoid any stops or traffic lights. Waze has been known to suggest this, and also known to revert to waiting at lights when better average speed information is collected from the side streets. But note that this can be less than optimal due to the turn delays discussed above.
 
== Outdated and abnormal road speeds ==
Road conditions change, construction work comes and goes, and average road speeds can change dramatically. One day you might be stuck behind a truck, and another day you might be crawling along the roads at 2 a.m. transporting your pet goldfish. Or your GPS might have a glitch and show you travelling at 1,000 mph.
 
In short, average speeds can change over time, and recorded times can be abnormal or just plain wrong—and can stay wrong for a very long time.
 
We can assume Waze is aware of this. There is some evidence that abnormal road speeds and old road speeds are discarded, or at least not used in calculating the average speeds of roads.
 
== Average road speed "shrinking window" ==
If there are enough recorded speeds on a road, then Waze uses a shrinking window of speeds to better estimate the average speed at the time you are travelling on it. Waze uses the speed of each road segment (in both directions) in intervals as small as 30 minutes. So a two-way road might have up to 96 average road speeds. We can assume that when there are insufficient records for an individual time slot, a wider time range is used (up to a full day). As the road is driven more, the time slot shrinks down to 30 minutes.
 
We can speculate that there is additional information used that is based upon the day of the week. There is some observational evidence that a road that is busy on weekdays and not used for routing is chosen as the optimal route on weekends.
 
At some point, Waze also needs to consider the months of the year as seasonal variations can affect the speed of the roads.
 
Waze uses the average road segment speed for the time slot that applies at the time you are expected to arrive at that road segment.
 
Because of this "time window", Waze suggests different routes at different times of day. This is dependent on how many times are recorded on the roads along the route. If they're all recorded at about the same time of day, then the time window does not help. If 1,000 times are recorded at about 5 p.m. and 2 times are recorded at 10 a.m., then your 10 a.m. average speed still is based mostly on times from around 5 p.m.
 
== Routing algorithm refinements ==
=== Routing options ===
It's easy to see how routing options can be implemented. For example, to minimize turns we can add a time [[Routing_penalties|penalty]] for fastest routing or a distance penalty for shortest routing, when calculating the fastest or shortest route.
 
=== Junction penalties ===
For newly created roads, currently Waze applies a five-second time [[Routing_penalties|penalty]] for each junction through which a route passes. Once vehicles drive over that road and generate Waze traffic data, the penalty for these junctions is dropped.
== What to do if you think the generated route is wrong ==
Firstly, use # Use the option to generate alternative routes. This might give you some clues as to why Waze is offering that route. Secondly, if # If you think there is a better route, check in WME the [[Waze Map Editor]] that the all of its roads are connected, and all connected along legal turns are allowed.# Communicate the routeproblem.Possible means of communication include:#* Report a [[map issue]] in the app and respond to comments on it.Thirdly, post #* Post a message detailing the problem route - (origin, destination and a WME permalink ) to the [http://www.waze.com/forum/viewforum.php?f=6&sid=2872533f5796ac39dc6747511398e907 Navigation forum]. Other eyes will check it, and you might indeed find a flaw in the Waze routing algorithm. Fixing it might make it better for everyoneor your state's local forum== Change of routing ==When #* Join your local community's Waze receives notification of traffic conditions it uses the actual speed of roads on Discord server (accessible from your route, rather than the average speedstate wiki page). This is based only on will usually produce the automatic traffic condition reports - light, moderate, heavy traffic or complete standstill. Manual reports of traffic jams and accidents are for your information only and do not change routing. It might be that even with the traffic reports, there is no better route and Waze cannot offer you onefastest response from local editors.
== You are the driver ==
Waze can never see that the traffic light is green going straight, or know that today is a public holiday. It can offer you guidance as to what is the best route under average conditions. But you are the driver and you are in the best position to make the decision for today under today's conditions.
If everyone followed Waze directions and never drove on a new route, Waze might never learn that route is better. When Waze is recording your travels, every trip helps make Waze better for everyone. That includes when you think you know better. Sometimes you will be right. And sometimes you will be wrong. But it is better to find out you are wrong so you can choose the better route. And when you are right, all Waze users benefit by the sharing of your knowledge.
[[Category:Waze operations]]
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