Transportation Technology Center, Inc. conducted a series of experiments between April 2012 and January 2014 to determine train characteristics and track conditions that affect shunting performance at two revenue service test locations. Optimization of track circuits for train detection is an ongoing effort by the railways and signal equipment suppliers. Most track circuits can be made more effective by having clean ballast and good track drainage. Whetting currents increase the sensitivity of track circuits to shunting and are used effectively at many locations. Use of signal averaging on island circuits has also improved shunt reliability.