Time windows
What are time windows?
A time window is the period between a start and end time in which a network location, such as a stop in a route analysis, should be visited by a route.
Two network analysis layers incorporate time windows: route and vehicle routing problem layers. The next two tables provide an inventory of the network analysis classes that you can set time windows for.
|
Network analysis class |
Time window field |
|---|---|
|
Stops |
TimeWindowStart |
|
TimeWindowEnd |
Note:The time window start and end properties are only visible in a stop's Properties window if the analysis layer property, Use Time Windows, is checked.
|
Network analysis class |
Time window field |
|---|---|
|
Orders |
TimeWindowStart1 |
|
TimeWindowEnd1 |
|
|
TimeWindowStart2 |
|
|
TimeWindowEnd2 |
|
|
Depots |
TimeWindowStart1 |
|
TimeWindowEnd1 |
|
|
TimeWindowStart2 |
|
|
TimeWindowEnd2 |
|
|
Breaks |
TimeWindowStart |
|
TimeWindowEnd |
You don't have to check any properties in the vehicle routing problem analysis layer to make time windows available; they are always available. Orders and depots allow you to set two different time windows; each of their time windows is grouped by the number at the end of the time-window field names.
Route objects in the vehicle routing problem also have time window fields: EarliestStartTime and LatestStartTime. They specify the period in which a route can begin its journey.
A time-window example
To better understand time windows, take the example of four stops—a, b, c, and d—for which a route needs to be found. The time window for each stop is given by its TimeWindowStart and TimeWindowEnd properties.
 |
The route can begin from point a at any time between 8:00 and 9:00 a.m. However, it should not reach b before 9:10 a.m. As shown below, the route reaches b at 9:05:08 a.m.
 |
Since b should be visited only between 9:10 and 9:12 a.m., the route waits at b for 4 minutes and 40 seconds and departs at 9:10 a.m. This wait time is stored in the Wait_Drivetime property of stop b as 4.66 minutes, and is added to the total time taken for the route. The property Cumul_Drivetime for a stop stores the total time taken to reach it. The Cumul_Drivetime of b is 10 minutes (5 minutes and 20 seconds of travel and 4 minutes and 40 seconds of waiting to honor the time window of stop b).
 |
The route departs from stop b at 9:10 a.m. and reaches stop c at 9:15:20 a.m. However, stop c has a time window of 9:10 to 9:12 a.m. There is a violation of 3 minutes and 20 seconds, which is stored in Violation_Drivetime property as 3.33 minutes, since the route is unable to honor the time window of stop c.
Stop c is symbolized with the time violation symbol 
.
Time windows are treated as a "soft" constraint. This means that although the solver attempts to honor time windows, if necessary, it will violate the time windows of some stops in order to reach them. This is different from a "hard" constraint in which there will be no route to the stop that has a time window violation. Hard time windows are not supported by ArcGIS Network Analyst.
A route solver attempts to find the least-cost route through a series of stops while respecting chosen restrictions on the network and honoring all time windows. If time window violations are inevitable, the solver attempts to minimize the total violation time.
Time windows with historical traffic data
If your network dataset has a time-zone network attribute, which is used with historical traffic data, any network locations with time-of-day or date field refer to the time zone of the edges they are located on.