Traffic data

You can bring up comments or questions about this in  Traffic Data forum topic.

This is all very unformed, and I have probably got most of it wrong, or out of context.

Do not use the information found here to make any decisions about Waze editing.

Over time, I will refine this information by asking questions of those who know more than I do. When the information is closer to correct, I will change the disclaimer at the top.

This article is about how editing roads affects the stored traffic data and Waze routing. For information on what Waze does with your personal information and how that can affect you, please read the Waze privacy policy and a community-created discussion of how this can affect you for more information on your privacy while using waze.

What Waze Map Editors Need to know about how traffic data is stored

The Waze map editor's motto is "usability, simplicity, retention". What we want to retain is the traffic data the Waze servers use for determining the best routes. In order to develop useful guidelines and best practices, we must understand what information is stored and what happens to it when we junction,disconnect, cut, merge, shrink, stretch, add or remove geometry nodes, change the direction (unknown, one way, reverse direction, two-way). Of course, Waze chooses to keep some details about its routing algorithms (and the data those algorithms use) secret, so you won't find those details here.

Glossary

Segment cross speed

The average speed at which wazers traverse the segment from A to B or from B to A during each time slice (fraction of day / day of week), not counting the additional time it takes to transition from one segment to the next.

Segment cross time

The average time it takes for a wazer to traverse the segment from A to B or from B to A during each time slice (fraction of day / day of week). Calculated from segment cross speed and segment length.

Transition time

The average additional time it takes to transition from one segment to another, in addition to the segment cross time. If the average segment cross for segment 1 time is 30s and the transition time from segment 1 to segment 2 is 30s, then the average total time it takes to enter segment 1 until entering segment 2 is 60s (during that time slice).

What information is stored

• For each segment, an average speed to traverse the segment in each direction (A to B and B to A) is stored, for many different times of day and each day of the week (time slices). In the past, Waze has referred to these as Forward Cross Speed and Backwards Cross Speed. Scripts like route speeds can get the speed for every half hour for every day of the week. From livemap, we can get routes for any half-hour time period during the day. WME Scripts like route speeds can obtain these cross speeds.
• In addition, we have been told that "transition time" is stored. This is the additional time it takes to go from the segment to any one of the other segments the current segment is connected to at a specific junction node. We do not know of any way access to these transition times via scripts like route speeds.
• Time to traverse a segment can be calculated from speed times length. The total time to cross segment 1 in the A-B direction and get to segment 2 is the segment 1 Forward Cross Speed + transition time to segment 2.
• We do not now how these numbers are calculated, what happens when wazers leave a segment before they get to the end, turn off their phone, or lose cell service. We don't know whether waze stores a lot of historical speeds and times or just keeps a running average, and whether it keeps data for more times of day then the 48 half-hour periods it shares with us.

What happens to traffic data when you make changes to the roads

• When you delete a segment (let's call it segment 100)
  • its cross times and transition times to other segments is deleted.
  • all transition times from other segments to that segment are lost; waze does not remember "turning left from segment 101 is a long wait" it remembers "the transition time from segment 101 to segment 100 is 3 minutes at 5:30 PM". If you delete segment 100, it can no longer use that information.
  • When you delete and replace a segment, waze has to start from scratch collecting data on segment cross time and also time to make turns from other segments onto that segment.
• When you shift the position of a junction without disconnecting anything, changing the lengths of several segments
  • The cross speeds are not changed.
  • Cross times calculations will change because the lengths of the segments has changed
  • Transition times are not affected.

When is traffic data lost?

• When you delete a segment, all traffic data involving that segment is lost
• When you disconnect a segment at a junction, all transition (turn wait time) data into and out of that end of the segment is lost.

Questions; what happens when

• Change the segment's length without moving the ends, as by stretching out a geometry node.
  • Same cross speed is used, so the calculated cross time will change (?)
  • transition times are unaffected.
• Turn a turn green arrow red -- does anything happen to the already-stored transition time or cross speed? Does anything change about how data related to that segment is collected and stored when that red arrow transition is traversed?
• Turn a red arrow green. See above.
• Change a 2-way segment to 1 way.
• After a period of time (minute, day, month, year,) reverse the direction of the 1-way segment
• Cut a segment into 2 shorter segments without changing either of the 2 original junctions
• 2 segments junction; no other segments connected to that junction -- delete the junction -- what happens to cross speed. What happens to the "lost" transition times? What happens to the transition times that are not lost?
• disconnect a segment from a junction
  • and reconnect it before saving.
  • and save it disconnected, but reconnect it and save again before the next tile update
  • and save it disconnected through the next tile update, then reconnect directly after tile update.
  • for a few days, weeks, or months -- as a way to close a road during construction.
    • and then reconnect it to the same junction (nothing else having changed at that junction in the meantime)
• Connect a segment to a junction
  • a former "dead-end" node of an existing segment
• Snap two junctions together, creating one junction where there were formerly 2 junctions, without disconnecting any of the segments from either of the junctions.
• convert a bow tie junction to a "H" junction by the following method
  1. disconnect segment 1 from the bow tie junction
  2. connect segment 1 to the cross segment to create a new junction
  3. disconnect segment 2 from the bow tie junction
  4. connect segment 2 to the new junction.
• convert a bow tie junction to a "H" junction by the following method
  1. bridge segment 1 to segment 2
  2. move the joined segment to the new junction location on the cross segment
  3. reduce the elevation to ground and use the "junction" icon to create the new junction.

Things I've heard about traffic data

A segment stores average traverse speed to each of the connected segments, for each available time slot. When split cut , that speed is split cut by ??? percentage wise and applied to both new segments, same when stretched, the speed is kept proportionated to the original.

??? Kept proportional to original, or speed is copied to the newly -created segments?

If [I] understand things correctly, the speed data for a segment is not exactly portable. It's very junction dependent. In other words, it's not just the time lapse of traversing the segment in a particular direction, but what happens as a particular segment transitions to another particular segment. Once you detach and connect to another junction, Waze no longer knows comparative times to turn left, right, or continue. For this reason, there can be strategic decisions in terms of which ends of segments to leave connected and which to move around.

Q: [Are you going to ]lose turn data by disconnecting and reconnecting to the same junction?
A: by disconnecting and reconnecting to the same junction? I doubt that very much or at least sorta much

portability of speed data, ... [has Waze said?] in so many words that it is not, and that that is why it is VERY much discouraged for us to disconnect things if we ever plan to reconnect them.

thats different ... disconnecting through hte course of tile builds

if you are splitting dividing a road properly, you will not save with anything disconnected, let alone allow it through a tile build ... suppose it's more important for transition speeds

There are methods of closing roads that don't require any data loss.