This manual defines relay interface panels which only pass railroad preemption inputs through to the traffic signal controller, as passive-style interfaces. With passive-style interfaces, the traffic signal controller is responsible for processing all railroad inputs from the interface and managing the preemption operations. Off-the-shelf, passive-style interfaces are available, but can require complex logic processing in the traffic signal controller to provide the necessary preemption functionality. As a result of this, along with the possibility of equipment failure and potential human error, TxDOT does not allow passive-style railroad interface panels. The designer shall not specify use of a passive-style railroad interface panel without a design exception and verification that the interface panel can provide the output as described in Chapter 5, Section 4.