The system designer is obliged to consider the signaling technology available to provide the desired system operating performance at the least total cost. Within the scope of light rail transit applications, a well-established catalogue of proven technology is available.
Transit signal system design must consider not only what technology is available, but also the most rational combination of equipment for a particular application. Signal systems are customized or specified by each transit system to provide safe operation at an enhanced speed. The location of signal block boundaries is based on headway requirements and other considerations such as locations of station stops, terminals, highway crossings, storage tracks and special interlocking operating requirements.
Selection and spacing of track circuits for AC and DC propulsion systems are influenced by many factors. These include the degree of detection required for broken rails or defective insulated joints, the level of stray current control required, the frequency of interfering sources of power (propulsion and cab signaling), location of cross bonding, unbalance of track circuits, and the inherent advantages of various types of track circuits.
