High resolution traffic and signal event data

          The High resolution traffic and signal event data is collected by the data collection unit, which consists of an industrial PC and a data acquisition card. At each intersection, an industrial PC with a data acquisition card is installed, and event data collected at each intersection is transmitted to the data server in the master controller cabinet through the existing communication line (in this case, spare twisted pair) between signalized intersections. The data acquisition card (PCI-6511 from National Instruments) used in the system has 64 input channels. If the total number of detector inputs and signal phases for one intersection exceeds 64, an additional data acquisition card needs to be installed. A terminal box is used to limit the input direct current (DC) to a safe range and build the connection between the data acquisition card and the back panel of the cabinet. The terminal box allows digital voltage changes on the back panel, which indicate different traffic events in the field, to be captured by the data acquisition card installed in the industrial PC. A traffic event recorder software program, developed using the Microsoft Visual C# program, runs on the industrial PC in the field to record the events (for example, a phase 1 green change from “ON” to “OFF”) into a log file.
          Data communication between two controller cabinets is done using the existing twisted pair communication lines. A protocol of RS-485 is used to transmit data and synchronize time between cabinets. After the data in the local cabinets is transferred to the master cabinet, DSL or a wireless unit installed in the master cabinet is used to send the data back to the database located at the University of Minnesota. A sample of data is shown in the following figure. Each logged event starts with a time stamp that includes the date, hour, minute, second and millisecond based on the computer system time, followed by different types of event data including phase changes, detector actuation, and pedestrian calls. A complete history of traffic signal events is thus recorded.