Fig. 5 Automatic block system for double track sections
b. Block systems for single track sections
Single-track sections differ from double-track sections in that trains are operated in both inbound and outbound directions over a single main track. Therefore, these systems require block functions not only for continuing trains but also for opposing trains. The main types of block systems used for single-track sections are described below.
(a) Automatic block system (type A)
This system is used for trunk lines. Like automatic block systems for double-track sections, track circuits are installed continuously in and between stations to automatically control home, departure and block signals.
Fig. 6 Automatic block system (type A)
(b) Automatic block system (type B)
This system treats the block section between stations as a single block section, and is used on auxiliary trunk lines where there is relatively little traffic demand.
This system creates one long distance track circuit between stations. Therefore, in contrast to automatic block system type A, signals are laid out only in the stations and uses distant signals.
