4 The Block System for Local Single-track Sections
There is a concept referred to as "track capacity", meaning the maximum number of trains which can be run on a given railroad track per day. Factors affecting track capacity are the running time between stations, block types, speed ratio of each train and provision of shunting facilities. Table 3 shows a rough calculation of track capacity based on the relationship between the block system and running time between stations.
Table 3 Sample track capacity (Total up & down)
Track capacity equation for single track
N: track capacity between stations (number of trains/day)
T: average running time of one train between stations (minutes)
C: block handling time (minutes)
In the case of a tablet block system, 2 minutes and 30 seconds.
In the case of an automatic block system, 1 minute and 30 seconds.
f: coefficient of track utilization
Usually, a value between 0.5 and 0.75 is used depending on characteristics of a line area.
In order to increase the track capacity of a single-track section, the running time between stations "T" and the block handling time "C" must be shortened as indicated in the equation above. A tablet block system has shortcomings in the form of a large value "C" and the lack of interlocking with signals.
A tokenless (semi-automatic) block system, which ensures the block procedure electrically instead of with a "token" carried by the train driver can be adopted in a single-track section. This system is broadly classified into two types; a continuous-train-detect type using a track circuit between stations, and a check-in/check-out type using a set of short-length track circuits (open/closed) or axle counters at the exit point of stations. A long-distance track circuit using 25/30 Hz (max. 5 km for electrified sections) was developed for the former type.
