(Redirected from Junction penalties)
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 The information on this page is subject to change, and any information that has been revealed may be incomplete or out of date.
- 1 Client-based routing
- 2 Routing requests
- 3 Different route lengths
- 4 Real-time current road speeds
- 5 Average road speeds
- 6 Recalculation
- 7 Traffic lights and stop signs
- 8 What to do if you think the generated route is wrong
- 9 You are the driver
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.
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
- Whether to avoid
- 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
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 routing road type, so a Primary Street with routing road type +1 would be pruned at the same threshold as a Minor Highway., and , respectively. There is evidence that is never pruned. and are never pruned. The pruning mechanism uniquely accounts for
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.
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.
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.
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.
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.
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
- 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 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.