1.1 - Provide Traffic Surveillance DFDThis DFD shows the processes that make up the Provide Traffic Surveillance facility within the Manage Traffic function. These processes collect and store traffic data collected by sensors for use in traffic management, and by the media and other ITS functions. They are also responsible for using the data to generate a predictive model of network operation and for the exchange of data with Manage Traffic functions serving other areas.
The key points about the facility are as follows:
- Data collected about the passage of vehicles and pedestrians through the surface street and freeway network;
- Collected data is stored as either current data (five minutes old) or long term (historic) data;
- Collected data used by the Provide Device Control facility to control vehicles and pedestrians;
- Predictive model produced using long term data and data from other traffic management centers;
- Predictive model data used by the Manage Travel Demand and Route Selection facilities;
- Many ITS functions use the current, long term and predictive data stores as a source of traffic data;
- Traffic operations personnel can display current, long term and predicted data;
- Output sent to the media;
- Traffic probe data collected from vehicles and provided both for storage and for output;
- Environmental probe data collected from vehicles and provided for output to other processes, and formatted for output to passing vehicles;
- Collected data and incident data is exchanged with other traffic management centers;
- Devices in other jurisdictions may be controlled by the local traffic management center, and vice versa.
There are seven processes in this DFD and three are separate DFDs:
a) Process Sensor Data (DFD 1.1.1)
b) Process and Store Traffic Data (DFD 1.1.2)
c) Generate Predictive Traffic Model (1.1.3)
d) Display and Output Traffic Data (DFD 1.1.4)
e) Exchange Data with Other Traffic Centers (1.1.5)
f) Collect Vehicle Traffic Probe Data (1.1.6)
g) Collect Vehicle Environmental Probe Data (1.1.7)
All data about vehicles and pedestrians passing through the surface street and freeway network is collected by processes (a), (f), and (g). It is then sent to processes in (b) which distribute it to other facilities and load it into the current and long term data stores. The data in these stores plus weather and incident data is used by process (c) to produce a predictive model of future traffic conditions. The results of this process and the data stored by processes in (b) are available for display by the traffic operations personnel and the media through the processes in (d). The long term data is also exchanged with other traffic centers, the data from which is also used as input to the predictive model by process (c).
Data is exchanged with other traffic management centers by process (e). This process also supports local control of field devices outside its jurisdiction (e.g., CCTVs, environmental sensors) and vice versa.
Although all of these processes, except (a), (f) and (g), depend on others in the group for data, they will each operate continuously and independently. This enables traffic data to be processed, stored, and accumulated in a timely fashion. Process (a) could be deployed on its own with some of the control processes in the Roadside Control facility - see DFD 1.2.7, to provide a roadside based traffic control facility with no links to any central system for coordination, fault reporting, etc.
Processes in (a) also controls the video cameras used for traffic surveillance. This enables them to be set up to collect traffic data from different “views”, where a “view” is a particular video image of part of the surface street and freeway network. The “view” being provided by a camera may be changed by either the traffic operations personnel or automatically as part of a traffic control strategy through a process in the Provide Device Control facility - see DFD 1.2. This enables the same camera to be used to gather different traffic data at different times of the day, days of the week, etc. One example is the data needed to monitor traffic flows in the morning and evening peak traffic periods may need to be obtained from different “views”.
DFD: 1.1 - Provide Traffic Surveillance
Parent DFD: 1 - Manage Traffic
- 1.1.1 - Process Sensor Data
- 1.1.2 - Process and Store Traffic Data
- 1.1.4 - Display and Output Traffic Data
PSpecs in this DFD:
- 1.1.3 - Generate Predictive Traffic Model
- 1.1.5 - Exchange Data with Other Traffic Centers
- 1.1.6 - Collect Vehicle Traffic Probe Data
- 1.1.7 - Collect Vehicle Environmental Probe Data