The Alaska Railroad Corporation (ARRC) decided to modernize the signaling system of the Anton Anderson Memorial tunnel, better known as Whittier Tunnel. At 13,300 feet, this is the second longest highway tunnel and longest combined rail and highway tunnel in North America. About 50,000 vehicles passing the tunnel per month make a reliable monitoring system absolutely vital.
The key point was to replace existing track circuits, which were deemed unreliable having less then optimal availability. Those had to be replaced with a more reliable and robust system, that would not be affected by water logging, moisture, fouled track, dirt crust or other contaminants within the tunnel.