2 ◾ Advances in Communications-Based Train Control Systems
the time interval (headway) between trains traveling along the line. Specically,
CBTC makes use of the communications between the railway track equipment
and the train for train control and trac management. Because the exact position
of a train is known more accurately than with the traditional signaling system, the
railway trac can be managed more eciently and safely.
As dened in the IEEE 1474 standard , a CBTC system is a “continuous,
automatic train control system utilizing high-resolution train location determina-
tion, independent of track circuits; continuous, high-capacity, bidirectional train-
to-wayside data communications; and trainborne and wayside processors capable
of implementing automatic train protection (ATP) functions, as well as optional
automatic train operation (ATO) and automatic train supervision (ATS) functions.”
In this chapter, we rst present the background and evolution of train signaling/
train control systems. en, we introduce CBTC systems, followed by the main
CBTC projects around the world.
1.2 Evolution of Train Signaling/Train Control Systems
e main objective of a train signaling/train control system is to prevent collisions
when trains travel on the railway track. erefore, a common ingredient of various
types of train signaling systems is as follows: the locations of the trains must be
known by the system at some level of granularity.
e rst generation of train control architecture includes track circuits for train
detection, wayside signals to provide movement authority indications to train oper-
ators, and trip stops to enforce a train stop . Figure1.1 illustrates this architec-
ture. In Figure1.1, if track circuit TC5 is occupied (shunted by a train), the signal
at the entrance to TC5 displays a red aspect. If block TC3 is unoccupied and TC5
is occupied, the entrance signal to TC3 displays a yellow aspect. If both TC1 and
TC3 are unoccupied, the entrance signal to TC1 displays a green aspect. ese
signals are separated by the train’s safe braking distance (SBD), which is calculated
and set at a sucient length for a train to stop safely from the maximum operating
speed specied for the track section. We can see that, in this system, a green aspect
means that two blocks (or at least twice SBD) are clear ahead of the signal; a yellow
aspect means that one block (at least SBD) is clear ahead of the signal; and a red
aspect means that the block ahead has a train occupying the track circuit.
Figure1.1 Train signaling system using wayside signals.