An extensive effort is needed to determine suitable timing plans for signalized intersections. Once a timing plan has been developed, it is often difficult to say whether or not it will actually work until it has been implemented in the field. The problems that result are addressed by adjusting the controller settings and timings. Traffic engineers would like the plan to work flawlessly in the field; unfortunately the reality is that frequent adjustments are needed. In order to save public agencies many problems, we attempt to make the major adjustments in the office or lab before field implementation.
These house the logic used to control the signalized intersections. If the signal control is pretimed then the controller determines when the signal indications should change based on fixed time settings. However, if the signal control is actuated the controller receives vehicle actuations from detectors at the intersection approaches, and then based on the user specified settings, the controller determines whether to continue a currently active phase or terminate it and begin another phase.
These provide the interface between the controller and the computer simulation, converting the simulation signals to signals that the controller understands and vice versa. This allows the simulation to send simulated actuations to the controller and to receive traffic control instructions from the controller that are based on the simulated actuations.
This computer runs the simulation of the traffic system shown on the far right side of Figure 1, generating a representation of traffic that occurs in the field. The traffic responds to the signal indicators displayed in the simulation.