The objective was to create an underground railroad traffic control system for unattended areas in a large mine.

This system consists of a light pod to be mounted at each end of a “block tunnel.”  The light pod would have a green (proceed) and red (stop) signal, so that approaching vehicles would know whether or not there was another vehicle in the tunnel; vehicles entering the tunnel are to manually trip a switch, thus sending a signal to both light pods in order to direct traffic flow.

The light pods and their switches are connected to a custom electrical enclosure (one at each end of the block tunnel) that houses switching relays and a Programmable Logic Controller (PLC).  These two PLCs communicate to each other in order to make sure that both light pods are displaying the same information, thus avoiding having multiple vehicles in the tunnel at the same time.

The objective was achieved, and several of these Pennsylvania Department of Environmental Protection Approved systems are in service in mines across Southwestern PA, with more being added as the mines expand.