Robert Burkhardt


Innovative Solutions in Signaling, LLC
United States

Houston Metro uses highly reliable axle counters for increased efficiency and punctuality


  • The Houston METRO Phase II project
  • System elements: Train control, communications systems, overhead catenary, traction power
  • Axle counter solution for vital signalling in interlocking and grade crossings as well as non-vital applications for train tracking and location


The Houston METRO Phase II project involved constructing 20 miles of new electrified light rail service on 3 corridors. This augmented METRO’s existing 7-1/2 mile system. Mass Electric (MEC) contracted to install all specialty systems elements: Train control, communications systems, overhead catenary, and traction power.

The final design included implementation of an axle counter solution for vital signalling in interlocking and grade crossings as well as non-vital applications for train tracking and location. An axle counting system consisting of approximately 550 wheel sensors were used on the project. Upon completion of the installation, the system was tested and commissioned and put into service. Shortly after operations began, an anomaly arose in which wheel sensing devices provided indication of train presence when trains were not in the vicinity (false occupancy). These false occupancies put the signal system into the safe condition to protect the interlockings as though a train were present. False occupancies due to miscounts, spurious failures, and calibration drift resulted in trains delayed at interlockings, crossing gates remaining down, and disruption to vehicular traffic that negatively affected METRO’s ability to operate the system.

Investigations and analysis did not identify the root cause of these false occupancies. The environmental conditions in Houston could have added to the cause. The environment has large temperature fluctuations and can experience significant rainfall that often results in flooding. This exposes WSD’s to prolonged submersion and temperature fluctuations.

METRO agreed to test alternative axle counter technologies. Frauscher and other suppliers installed test beds in the Downtown Corridor which were validated over a six month period. This test bed uncovered vehicle EMI issues as well as a number of other factors. The tests concluded that the Frauscher system experienced no unexplained false occupancies or failures.

The Frauscher system was selected for the replacement project based upon its performance and reliability. The Wheel Sensor RSR180 uses the same four-wire cabling, allowing the use of existing cabling and installed infrastructure. The evaluators and I/O modules provided the same implementation and interface as the original system. This resulted in a straight forward design and installation process.

A second Frauscher “test bed” was installed at a vital Northline interlocking to further verify the interface in a vital location. The system at Northline experienced several false occupancies. Investigation revealed that three LRVs were generating excessive EMI and causing these discrepancies. Frauscher testing led to a recommendation of a RSR180 variant that operates at a specific frequency. This device was less susceptible to the vehicle EMI and provided a better solution for METRO.

In advance of the replacement work, Frauscher provided engineering support and maintenance level training to MEC and METRO personnel. This allowed METRO to immediately begin maintaining the replacement system. Frauscher provided constant on-site support throughout the replacement process. This support ensured that replacement progressed smoothly and minimised the disruption to METRO’s operations. Work was completed in December of 2016 and to date has met or exceeded expectations.


Robert Burkhardt has been involved in railway signalling for more than forty years, the last fourteen years as president of Innovative Solutions in Signaling, a signalling design firm based in Louisville, Kentucky. A registered professional engineer and council member for the Institution of Railway Signal Engineers, he has a keen interest in signalling principles and equipment used in signal systems worldwide. As lead signal designer he directed the team that provided design for Houston Metro’s light rail expansion, one of the first projects in the US to utilize axle counters as the primary means of train detection throughout the system.

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