Tracking trains in Houston
The 51st Super Bowl, which welcomes 700 000 visitors, was the incentive to upgrade the Houston METRO. A new axle counter has further improved the efficiency, reliability and safety of the network.
The network of MetroRail Houston, or METRO for short, which was opened in 2004 and has since been extended across three lines, carries low-floor trains powered by an overhead line. The tracks run interchangeably as grooved rails, on concrete or in gravel beds. This variable track structure and the severe environmental conditions are a huge challenge for the outdoor equipment components. The same applies to the wheel sensors, which are used with axle counters for train detection purposes. As the system that had been used to date had been unable to handle these conditions satisfactorily, the operator decided to explore alternative options. The aim was to further improve operational safety for the 51st Super Bowl 2017, which welcomes several hundred thousand visitors to the city.
The infrastructure and environment of the Houston METRO are particular challenges for the signalling components.
Rain, heat and metal
Extreme heat, humidity, storms with heavy rain and local flooding characterise the weather in Houston. In particular, sensors in housings that are fitted to grooved rails must have adequate protection to prevent the ingress of moisture and must still be able to operate when immersed in water. Rainwater can also carry along metal debris, which is then mistakenly detected by the sensors.
Houston METRO defined a series of clear criteria for the implementation of a new train detection system. To ensure easy integration into the existing signalling system, it was essential to utilise the existing I/O inputs and cable systems so as to keep service interruptions to a minimum during the changeover. Quick delivery and commissioning was required in time for the Super Bowl, as the large sporting event was certainly going to challenge the public transport system in certain ways.
With this in mind, it stood to reason to evaluate alternative options that could make use of the existing system. The sensors needed to work effectively in busy areas where there are significant electromagnetic influences.
Frauscher reviewed the requirements and installed twelve RSR180 wheel sensors at six non safety-relevant locations for testing purposes. The evaluation was completed using the Frauscher Advanced Counter FAdC. Existing track holes were to be used when fitting the sensors. Frauscher therefore designed a special bracket for the RSR180, which could be mounted to existing holes. Due to the tight schedule, as the project progressed, the decision was made to use Frauscher’s proven SK140-010 rail claw, which had been developed specifically for use in situations where there is very little space between the rail and ground. Waiting for further development and approval of the prototype would have taken too long.
Following the initial successful results, another test installation was set up in the interlocking of the Northline Transit Center. The Frauscher Magnetic Noise Receiver MNR was used to analyse all METRO fleet vehicles. Based on the knowledge gained, Frauscher was able to choose a sensor with a special operating frequency to eliminate interference from the outset and guarantee optimum operation.
Wheel sensors fitted inside housings must operate reliably under a variety of conditions.
Minimum effort, maximum output
The tests carried out showed that the FAdC met all of the requirements with regard to environmental influences, interfaces, reliability and simple integration into the existing infrastructure. The axle counter’s flexible design enables efficient data transfer via a relay interface to the traffic control system and interlocking. The cable system only had to be slightly modified and the installation work only had minimal impact on operations.
In addition, two intelligent functions of Frauscher’s axle counter were used to tackle unexpected impacts: the Supervisor Track Section STS allows operation to continue when faults from external sources occur, by combining two track sections in a virtual section. It is then activated when a fault occurs on a section. This increases the system’s availability considerably without affecting safety or having to install additional equipment and incurring additional costs.
The SIL 4 compliant and patented Counting Head Control CHC function is used to avoid errors caused by unavoidable influences. If adjacent sections are clear, the wheel sensor switches to stand-by mode in which a freely configurable number of unwanted damping, from either metal waste or steel-toe capped boots, can be suppressed. As a result, no fault or occupied indication is generated and a reset is not necessary either. Approaching vehicles deactivate the stand-by mode and are safely detected. The Frauscher Diagnostic System FDS also provides diagnostic data, which can be used to constantly monitor the status and functionality of the axle counter. Selective and regular maintenance work can thereby be coordinated and planned very efficiently.
The robustness of the RSR180 wheel sensors and the improved availability of the FAdC contributed significantly towards better punctuality during operation. This is how the Houston METRO successfully transported more than 700 000 passengers through the city during the sporting event – a successful kick-off for the public transport system for the 51st Super Bowl.
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