Difference between revisions of "Routing server"

From Wazeopedia
(Fastest routing)
m (Pruning: wordsmithery)
(Tags: national guidance change, Visual edit)
 
(69 intermediate revisions by 19 users not shown)
Line 1: Line 1:
 +
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. 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 The information on this page is subject to change, and any information that has been revealed may be incomplete or out of date.
  
==Cálculo de una ruta==
+
== 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 closures, because this information is not accessible. Therefore, it does not provide an ETA.
  
 +
== Routing requests ==
 +
When a user requests a route calculation with a network connection, the request is sent to the Waze server. That route is then transmitted back to the client device and displayed.
  
Cálcular  una ruta óptima es una tarea difícil. Si bien la aplicación en el dispositivo (cliente) incluye un algoritmo de enrutamiento que sólo se activa si hay una conexión con el servidor de Waze.
+
The requests for routing vary according to the settings chosen for the user's account on the client device. Under Navigation one can choose:
 +
* 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 {{Ferry|Ferries}}
 +
* Whether to avoid {{Freeway|Freeways}}
 +
* Whether to allow, never allow, or avoid long unpaved roads
 +
* Whether to 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.
  
== Especulaciones ==
+
== 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.
  
El algoritmo de enrutamiento que utiliza el servidor de Waze no es de conocimiento para el público por lo que lo descrito a continuación, se basa en a en la observación, la especulación, y alguna información revelada por el personal de Waze. Podemos suponer que el funcionamiento del servidor de enrutamiento es la estrategia de Waze para competir frente otros navegadores. También podemos suponer que está sujeto a cambios, y que cualquier información que revelada puede ser incompleta o fuera de fecha
+
=== 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.
  
==Solicitud de ruta de navegación ==
+
== 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.
  
Cuando se solicita un cálculo de la ruta, ésta se envía al servidor de Waze. Esa ruta se transmite de nuevo a su [[dispositivo cliente]] y se muestra.
+
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.
  
Las rutas mostradas van a variar en función de las opciones de configuración seleccionadas en el dispositivo [cliente]. En virtud de enrutamiento puede elegir:
+
As the number and density of Wazers grows, this real-time data takes on a greater importance. This emphasis is partly a reflection of Waze's original goal to create optimal commutes. As Waze has grown to be used as a more general-purpose GPS navigation device over roads less traveled, the historical average road speeds becomes more important.
* La ruta más rápida o más corta
 
* Permitir o no, el acceso a través de caminos de tierra,  
 
* Utilizar el menor número de giros
 
* Evitar las autopistas (peajes ?)
 
* O seleccionar rutas para ir comiendo galletas (da mas puntos)
 
  
La ruta más corta se refiere a la distancia física. La mejor opción es seleccionar la ruta más rápida. (100 km de autopista es mejor que 90 km de caminos rurales).
+
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.
  
Las galletas (Cookie munchin)aparecen en caminos que no han sido recorridos. Cuando se activa esta opción, la ruta tserá menos directa para viajar por caminos sin confirmar, (y vas sumando puntos). Normalmente, esto incrementa en 10 minutos el recorrido, lo xual s poco importante en recorridos largos, pero si en los cortos . (un viaje de 3 horas se convierte en 3 horas y 10 minutos. Pero 20 minutos en coche se convierte en 30 minutos en coche).
+
== Average road speeds ==
 +
If the average or historical road speed is not correct, then the route may not be optimal. However, deletion of segments to reset average road speed is 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 Waze appears to disfavor the use of certain segments along a route, a number of other reasons can cause such a situation.
  
 +
=== 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 this road. As more people drive this road closer to the time of day when a given route is requested, Waze will get a better guess for the average speed at that time.
  
 +
=== 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 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.
  
== Carreteras "perdidas" y uniones incorrectas ==
+
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. 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.
Waze trata de encontrar la ruta más rápida a tu destino. Obviamente, pero escogerá una ruta alternativa , si la ruta  óptima no tiene las carreteras con todas las conexiones correctas en el[[Mapa en Vivo]]
 
  
==Velocidad de tráfico en tiempo real==  
+
=== Turn delays ===
Waze utiliza informes las velocidades en carretera en tiempo real en vez de las velocidades medias históricas de carretera. También utiliza los informes de congestión de tráfico para desviar la ruta evitando los tramos de tráfico lento. Las primeras versiones del cliente también informaban cuando la velocidad del tráfico era adecuada - pero se eliminó porque saturaban el mapa. Waze continúa recibiendo esta información. Podemos suponer que la velocidad de cualquier Wazer delante de ti en un tramo de la carretera es la velocidad que se utiliza para calcular tu la ruta.
+
On a segment of a road, a user's average speed can be very different depending on what 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.
  
A medida que el número y densidad de wazers aumenta, los datos en tiempo real adquieren una mayor importancia y son el objetivo de Waze para optimizar los traslados. Como el uso de Waze se está generalizando y se está utilizando como dispositivo de navegación GPS por carreteras poco transitadas, las velocidades medias históricas en estas carretera se consideran más importante.
+
[[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:
Desde Waze utiliza el tiempo de permanencia en un segmento de la carretera para calcular la velocidad en ese segmento, por lo que no puede utilizar los datos en tiempo real  para calcular la duración de un viaje en un intervalo de tiempo futuro. Así que los viajes de más de 30 minutos (y, en promedio, más de 15 minutos) pueden incluir errores de cálculo, dado que no se disponen en el momento de iniciar la ruta de las velocidades medias que habrá en los distintos tramos de la ruta cuando se vaya a circular por ellos. Por eso, a medida que se va avanzado sobre la ruta calculada, se irán recalculando los tiempos , en función de los datos de velocidades que se vayan presentando en cada momento.
 
  
==Rutas mas rápidas==
+
* Seg4 to Jnct2 to Seg5
WThis means if it already knows the best route from B to C, and you ask for a route from A to C, it may 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 may 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.
+
* Seg4 to Jnct2 to Seg6
  
Waze conoce la velocidad media de todas las carreteras "confirmadas" a tu destino. El servidor de Waze puede calcular la lista de rutas a tomar para minimizar el tiempo total de viaje.
+
Traffic building up on Seg4 that turns right to Seg6 does not affect the route timing for the traffic also using Seg4, but instead turning left to Seg5.
Mientras que cada solicitud se procesa en tiempo real, por observación, parece que Waze almacena algunas rutas solicitadas o puntos importantes. Esto significa que si ya conoce la mejor ruta de B a C, y se solicita una ruta de A a C, sólo se puede calcular la mejor ruta de A a B, una vez que se comprueba que no hay una mejor ruta sin pasar por B. Esto quiere decir que hay un periodo de tiempo hasta la actualización del [[Mapa en Vivo]]que  algunas rutas serán menos óptimas hasta el día que estén almacenadas y realculadas.
+
For this reason it is important to keep long segment lengths before junctions as traffic congestion at the junction might affect exits differently.  
  
Mientras , mediante un cálculo complejo, es posible el cálculo de la ruta óptima . La complejidad surge en torno a la "velocidad media" de las carreteras.
+
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 &mdash; 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, the segment before the junction should be kept long, or a [[junction box]] may be used.
  
==Changes in route due to different [[glossary|origin]]==
+
=== Outdated and abnormal road speeds ===
Consider calculating a route from A to Z. The suggested route may be A to B to C to D to Z. Then calculate the route from B to Z. You may get a suggested route of B to C to E to Z. At first glance, this suggests one route is not optimal.
+
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 used in calculating the average speeds of roads.
  
We can guess at what might be happening. There may be a problem associated with the possible caching of routes. Or there may be a "timing window" effect. The different arrival time at C may change the best route to Z. Or there may 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.
+
== Recalculation ==
 +
When Waze receives notification of traffic conditions, 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 and do not change routing.
  
This effect can be observing while driving. If you recalculate a route to a destination while driving along an already calculated route to that same destination, the route may change.
+
ETA is updated in response to a user's progress on the route 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.
  
This are old reports where wazers have not offered a route to bypass heavy traffic but do receive a new route when manually asking for it. It may be they would have been offered that alternative route at that point anyway, whether or not there was bad traffic ahead. It does raise question as to when and how Waze considers rerouting but these may have been addressed in the current version. Certainly Waze does offer new routes sometimes.
+
== Traffic lights and stop signs ==
 
 
==Changes in routes due to different route lengths==
 
 
 
In addition, it is known that the Waze routing engine can't calculate every possible route for long distance routes, so takes shortcuts for longer routes, potentially resulting in the route changing dramatically when lengthened slightly. According to Waze support (as of July 2011), the section of a route more than 10 km from each endpoint is heavily weighted towards non-streets (i.e. "Primary Streets" or the various Highway types). My personal guess is that it simply ignores streets outside of the 10 km radius from the endpoints when doing its calculations to speed up the calculation. The specific quote from support was:
 
"Above some distance (currently 10KM) from both end points (start and destination) the server prefers to go through non streets. Now as it happens here - this small distance was the difference between being less than or over 10KM. Now the penalty of going through a street in this case is high - so the server prefers the highway." In this particular case, the observed behavior was that extending the route by a short distance caused Waze to suggest a very different (and much longer, both in distance and estimated time) route.
 
 
 
==Problems with average road speeds==
 
If the average road speed is not correct, then the route will not be optimal. The following are reasons why using the average road speed can be the wrong value to use.
 
===Time of day variations===
 
Consider a road that most wazers drive at 5pm when the average speed is 12 mph. You choose your route at 10am when the road is clear and the average speed is 60mph. It is the best road to take, but Waze chooses a different route because it has no information about the speed at 10am and assumes the speeds is 12mph all day.
 
 
 
You can, of course, drive the road yourself, and Waze will eventually learn. We do not know how many times Waze uses in its calculation. However if Waze does discard old time information, you may not accumulate new time faster than it is discarded. It is also possible that your times are being ignored as being abnormal.
 
 
 
More Waze users would help fix this.
 
===Turn delays===
 
Consider a road of length 1 mile where you drive straight ahead and go through the intersection all at 100mph taking 36 seconds. Or at the end of the road you can sit and wait 5 minutes to make a turn. In the first case your average speed is 100mph. In the second case your average speed is just under 11mph.
 
 
 
Now if 9/10 wazers go straight through, the average road speed is 91 mph. Waze will recommend this route, even if if involves a turn on your route, and the route is not optimal.
 
 
 
Contrariwise, if 9/10 wazers make that 5 minute turn, the average road speed is 20mph, and even though your optimal route would take you straight through at 100mph, Waze will not suggest it because it sees the average speed as 20 mph.
 
 
 
We can assume Waze is aware of this issue. You can choose the Minimize Turns option in your Routing settings. Or you can use your own discretion. The good news is that by collecting your route information Waze is collecting enough information to give correct routing advice when it implements it. It knows the average speed of people going straight through and it knows the average speed of people making the turn. And it can apply the correct average speed when calculating your best route. It make the calculation more complex, but it can be done.
 
 
 
At the moment it is not being done.
 
 
 
===[[Cartouche]] editing===
 
The average speed of a road can be dramatically altered by editing in Cartouche. Consider a 50m length of road driven in 36 seconds. An editor extends this length of road the full 10km length. Cartouche now records this road as 10km long but also driven in 36 seconds for an average road speed of 1000km/hour. This has been a particular problem as people adjust the length of ramps.
 
==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 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 long enough, a longer route that avoids the light will become the preferred route. This has been observed in practice and is an example of ''emergent behaviour''. Waze isn't programmed to avoid traffic lights but it will avoid slow roads; if the traffic lights make the road slow then Waze will avoid them.
+
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 behavior''. 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 will 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 back 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 may be stuck behind a truck, and another day you may 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 may have up to 48 average road speeds. We can assume that when there are insufficient records for an individual time slot, a wider time range is taken—up to a full day. As the road is driven more, the time slot would shrink down to 30 minutes.
 
 
 
We can speculate that there may be 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 will be chosen as the optimal route on weekends.
 
 
 
At some point, Waze would also need 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 will suggest 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 will 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 will still mostly be based 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 minimise turns we can add a time penalty for fastest routing or a distance penalty for shortest routing, when calculating the fastest or shortest route.
 
 
 
===Junction penalties===
 
Currently Waze applies a five-second time penalty when calculating a route that passes through a junction. While not an unreasonable approach to dealing with intersections, it has generated some flawed routing and is being reviewed. 
 
 
 
One major issue arises in long highways which may be made up of hundreds of segments connected together, as this may add a penalty of as much as five minutes to a trip, even though the intersections are not real. This supports the arguments of those who aim to have a clean edit of maps where junctions are only used when necessary. In practice, we need to deal with the map as it stands. An automated tool to remove the junctions is needed as the manual work that is required is enormous.
 
 
 
The routing problem can be fixed in a variety of ways. One could:
 
* Not apply the penalty when there are no other existing roads meeting at the junction;
 
* Not apply the penalty when you cross a junction onto a road with the same name;
 
* Not apply the penalty when the road you are travelling on is a higher class (e.g. highway versus street, primary street versus street), where we can assume the higher class road has the right of way; or
 
* Not apply the penalty at all when travelling on freeways, motorways and highways.
 
 
 
Even if a road is correctly connected with no unnecessary segments, the junction penalty can still give incorrect results. For example a busy highway may be correctly connected to the ramps along its length. A quiet country road running in parallel may not have all the minor connecting roads recorded; it looks like a straight section of road with no junctions. Waze may choose the country road as the preferred route because of the lack of junctions.
 
 
 
==What to do if you think the generated route is wrong==
 
Firstly, use the option to generate alternative routes. This may give you some clues as to why Waze is offering that route.
 
 
 
Secondly, if you think there is a better route, check in Cartouche that the roads are all connected along the route.
 
  
Thirdly, post a message detailing the problem route - origin, destination and a Cartouche [[permalink]] to the [http://www.waze.com/forum/viewforum.php?f=6&sid=2872533f5796ac39dc6747511398e907 Navigation forum]. Other eyes will check it, and you may indeed find a flaw in the Waze routing algorithm. Fixing it may make it better for everyone.
+
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.
  
==Change of Routing==
+
== What to do if you think the generated route is wrong ==
When Waze receives notification of traffic conditions it uses the actual speed of roads on your route, rather than the average speed. This is based only on 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.
+
# Use the option to generate alternative routes. This might give you some clues as to why Waze is offering that route.
 +
# If you think there is a better route, check in the [[Waze Map Editor]] that all of its roads are connected, and all legal turns are allowed.
 +
# Communicate the problem. Possible means of communication include:
 +
#* Report a [[map issue]] in the app and respond to comments on it.
 +
#* 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] or your state's local forum.
 +
#* Join your local community's Waze Discord server (accessible from your state wiki page). This will usually produce the fastest response from local editors.
  
It may be that even with the traffic reports, there is no better route and Waze will not offer you one.
+
== 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.
  
==You are the driver==
+
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.
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 may 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 benefits by sharing in your knowledge.
+
[[Category:Waze operations]]

Latest revision as of 01:49, 16 August 2019

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. 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, reports or closures, because this information is not accessible. Therefore, it does not provide an ETA.

Routing requests

When a user requests a route calculation with 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:

  • Whether to allow or avoid toll roads
  • Which, if any, toll and HOV passes to apply (some segments are permitted only to those who hold the proper pass)
  • Whether to avoid  • • • • Ferries • • • •  
  • Whether to avoid  Freeways 
  • Whether to allow, never allow, or avoid long unpaved roads
  • Whether to avoid difficult intersections (turns marked "difficult" through nodes or junction boxes).
  • Vehicle type

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 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. The speeds of recent Wazers traveling on a road will be factored into the route given to subsequent Wazers traveling on the same road.

As the number and density of Wazers grows, this real-time data takes on a greater importance. This emphasis is partly a reflection of Waze's original goal to create optimal commutes. As Waze has grown to be used as a more general-purpose GPS navigation device over roads less traveled, the historical average road speeds becomes more important.

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.

Average road speeds

If the average or historical road speed is not correct, then the route may not be optimal. However, deletion of segments to reset average road speed is 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 Waze appears to disfavor the use of certain segments along a route, a number of other reasons can cause such a situation.

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 this road. As more people drive this road closer to the time of day when a given route is requested, Waze will get a better guess for the average speed at that time.

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 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. 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, a user's average speed can be very different depending on what 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.

SegmentTraffic1.png
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:
  • Seg4 to Jnct2 to Seg5
  • Seg4 to Jnct2 to Seg6

Traffic building up on Seg4 that turns right to Seg6 does not affect the route timing for the traffic also using Seg4, but instead turning left to Seg5. 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, the segment before the junction should be kept long, or a junction box may be used.

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 segments are less than 19.69 ft (6 m) 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 used in calculating the average speeds of roads.

Recalculation

When Waze receives notification of traffic conditions, it uses the actual speed of roads on your route, rather than the average speed. This is based on 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 and do not change routing.

ETA is updated in response to a user's progress on the route 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 behavior. 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.

What to do if you think the generated route is wrong

  1. Use the option to generate alternative routes. This might give you some clues as to why Waze is offering that route.
  2. If you think there is a better route, check in the Waze Map Editor that all of its roads are connected, and all legal turns are allowed.
  3. Communicate the problem. Possible means of communication include:
    • Report a map issue in the app and respond to comments on it.
    • Post a message detailing the problem route (origin, destination and a WME permalink) to the Navigation forum or your state's local forum.
    • Join your local community's Waze Discord server (accessible from your state wiki page). This will usually produce the fastest 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.