Available with Network Analyst license.
This help topic provides information on how live traffic works. For an overview of traffic, see What is traffic data.
Live traffic attribute properties
The Live Traffic tab displays the properties that can be configured on a network dataset that supports live traffic.
Live traffic workflow
The network dataset reads live traffic speeds from dynamic traffic format (DTF) files and relates the speeds to edges using traffic message channel (TMC) codes. TMC codes are standard unique identifiers that are supported by various organizations, including traffic data providers. The following graphic and the text below illustrate and describe this process.
The network dataset queries an edge for the current travel time. This occurs when a network analysis layer is being solved or when traffic is being drawn on a map.
The identifying source feature information (source feature class, source feature, and from-to and to-from positions) is used to look up one or more TMC values. The lookup is performed with the information that was in the Streets-TMC Table at the time of the last network build. The Streets-TMC Table relates streets to TMC codes.
The red box around the Streets-TMC Join Table in the diagram is there to highlight an oversimplification of the diagram. A network dataset doesn't directly reference the join table during the query process; that would be too slow. Instead, the information in the join table is built into the network dataset and referenced internally for faster processing. Consequently, any changes you make to the Streets-TMC table won't be incorporated into the network until it is rebuilt.
The network dataset looks for a DTF file, which is a binary file designed for network datasets, and reads the travel speed information. The files are stored in a directory that you point the network dataset to using a local or UNC path. On the Live Traffic tab, you can specify the folder where the downloaded DTF files reside by clicking the browse button for the Dynamic traffic files location property.
Each DTF file is marked with a valid time range and contains TMCs and their corresponding travel speeds for the given time span. The network dataset opens a DTF file only if the time and date for which the edge is being queried is within the DTF file's valid time range. In many cases, multiple DTF files have valid time ranges that are within the queried time. This can occur when live traffic includes traffic predictions of a given depth, for example, for the next 12 hours. If multiple, valid files exist for the queried time, the file that was created immediately before the queried time is opened.
Only one DTF file is opened per solve. That is, if multiple, valid files exist, only one is used throughout the duration of that solve process. Whenever the solver queries an edge for a time and date that is outside the file's time range, it attempts to retrieve the travel time from historical traffic tables instead.
Once the DTF file is opened, the TMC and its associated travel speeds are combined with the length of the queried edge to determine the actual travel time.
If a valid TMC value or DTF file can't be found, the network dataset falls back to historical traffic to retrieve the travel time. If historical travel times don't exist, it falls back to either a weekend- or weekday-specific network cost attribute, depending on the day of the week for which the edge is being queried. This fallback sequence is set out in the edge traffic evaluators of the traffic-based cost attribute.
The Streets-TMC table furnishes the information needed to relate edges to speed values that are stored in DTF files. Typically, this table is provided by a data vendor along with street data.
The table below lists the required fields of a Streets-TMC table, an example field name, the allowed data types, and a short description.
The Network Analyst tutorial data, which is available on ArcGIS.com, includes a San Diego network dataset with a Streets-TMC table for your reference. After downloading and extracting the data, you can find the SanDiego geodatabase at \Network Analyst\Tutorial\SanDiego.gdb.
|Field||Field name example||Data type||Description|
Edge feature class identifier
You must name this field EdgeFCID.
Identifies the feature class that stores the street feature.
Edge feature identifier
You must name this field EdgeFID.
Identifies the street feature.
Edge from position
You must name this field EdgeFrmPos.
Works in conjunction with EdgeToPos to identify a direction of travel or side of the street. Zero indicates the beginning of the line feature as defined by its digitized direction. One indicates the opposite end.
For example, an EdgeFrmPos value of 0 and an EdgeToPos value of 1 identifies travel in the digitized direction of the line feature. The TMC value listed in the same record represents that side of the street only.
Any decimal values specify a position along the digitized direction of the feature, which allows the Dissolve Network tool to maintain the proper TMC values for streets after edges have been dissolved together.
Edge to position
You must name this field EdgeToPos.
Works in conjunction with EdgeFrmPos to identify a direction of travel or side of the street.
The TMC code representing the associated road segment.
Modify live traffic
To create a working live-traffic network dataset, the following items are required:
- A Streets-TMC table, which must be stored in the same geodatabase as the network dataset you are working with.
- A time-zone table, which must be stored in the same geodatabase as the network dataset you are working with. A time zone network attribute is created to get information from the table.
Note:Setting up live traffic is optional for traffic-enabled network datasets. You can skip configuring live traffic if your goal is to configure historical traffic only. When you configure live traffic, you must configure it in tandem with historical traffic.
Follow the steps below to modify a network's live traffic settings:
- Open the Network Dataset Properties dialog box.
- Click Traffic.
Two tabs, Historical Traffic and Live Traffic, appear. However, if the network dataset you're using was not configured to support traffic at the time it was created, these tabs will not be available.
- Click the Live Traffic tab.
- From the Streets-TMC Table drop-down list, choose the Streets-TMC table.
If your geodatabase does not have a valid Streets-TMC table candidate, the drop-down list will be empty.
DTF files created from traffic feeds store travel-speed information by TMC code. The Streets-TMC table relates TMC codes to street segments or subsections of street segments so that travel speeds can be linked ultimately to network edges. The Streets-TMC table is often included with network data acquired from a data vendor.
- From the TMC drop-down list, choose the field in the Streets-TMC table that contains TMC codes.
- For Dynamic traffic files location, type the path of the folder or browse to the location of the folder that contains dynamic traffic files.
The path to the folder can be a local file system path or a Universal Naming Convention (UNC) path.
Traffic files can only be specified as a folder location. If you have a service-based dynamic traffic files location on your network dataset, it will be present by default in the Dynamic traffic files location box and will be used in your analysis and traffic display. You can't delete this reference from the box. If you need to change the source for dynamic traffic files, browse to the folder location and select the appropriate folder.