A system for controlling traffic for allowing passage of an emergency vehicle through an intersection controlled by traffic signals includes an intersection module for transmitting signals for preempting the traffic signals and one or more circuit cards coupled to the intersection module. Each expansion card includes a plurality of contact closures for outputting one or more of the signals for preempting the traffic signals. The intersection module selects an expansion card based on a type of output desired, and further selects one or more contact closures of the selected card for the desired output. The expansion cards allow preempt or vehicle outputs beyond the output that a single card can provide. According to another embodiment, the output expansion is achieved by emulating the communication interface between the intersection module and the traffic signal controller.