7 Transition of Automatic Train Protection Devices
Signalling systems guarantee train operation safety as long as a driver runs the train obeying the signal aspect. As the train speed and frequency increase in a section, mis-operation by the driver may increase as well. Hence the need for an automatic train protection (ATP) system will be required sooner or later. In a wayside-signal system, the ATP system is added to the existing signalling system, on the other hand, in a cab-signal system, the ATP functions are internalized in the signalling system. In Japan, the former is defined as an ATS (Automatic Train Stop) system, and the latter as an ATC (Automatic Train Control) system.
Several types of cab-warning systems without the automatic-train-stop function were developed in the early stages, however, this was not enough to prevent the violation of signals by drivers. As a result of the train collision in Mikawashima station on the Joban line in 1962, the ATS-S ground-coil-detecting ATS system for general lines, and the ATS-B track-circuit-current-detecting ATS system for commuter lines were adopted nationwide in 1966. Fig. 14 shows the change in the number of train collisions and derailments before and after the ATS systems were installed, showing the significant effect they had.
Fig. 14 Train collisions and derailments
However, some shortcomings of the ATS-S system have gradually been revealed since. In this system, an emergency brake is automatically activated if no confirmation is given by the driver within 5 seconds after an alarm is given, regardless of the train speed. This means that the alarm is usually too early for high deceleration trains because the locations of ground coils for the alarm are the same as for low deceleration trains, the alarm of which only requires quick but easy confirmation from the driver.
The ATS-B systems on Yamanote and Keihin-Tohoku lines in the Tokyo area were replaced by the ATC system in 1981, taking into account past experience with the Shinkansen. The ATC system is suitable for sections running only integrated brake trains, and not for sections for multiple brake trains, for which another system has to be developed.
