Metro Rail News October 2017

Protection against Human Error – A general principal
within the safety community is, the less human
interaction, the safer it is. A conventional signalling
system depends on the operator to follow the rules of
the railroad. If an operator violates a safety critical
procedure (speed limit around a curve for example),
safety is compromised. Whereas a CBTC system is
automated and the human element is removed or
reduced significantly.
Comparison of Operational Characteristics
Out of the 11 safety features discussed above, 3 favor
CBTC, 1 favors conventional and the rest are neutral.
But when comparing the operational characteristics,
CBTC has the overwhelming advantage.
Operational Features
Conventional
CBTC
Maximize Throughput No Yes
Equipment & Maintenance
Significant/ Limited/
High Low
Automatic Speed
Regulation (Ride Quality) No Yes
Bi-Directional Operations No Yes
Reduced wear and tear of
train propulsion and
braking system No Yes
Energy optimization No Yes
Interoperability Yes No
Automatic recovery from
perturbations Limited Yes
Hint:
Red – Advantage for CBTC Signalling
Blue - Advantage for conventional Signalling
Black - Neutral
Maximize Throughput – Throughput is the primary
reason why CBTC is selected by transit authorities.
Its ability to reduce headways is unmatched by any
conventional signalling technology available on the
market today.
Equipment & Maintenance – A track littered with
signals, trip stops, track circuits, associated cables
and row upon row of relay racks in the equipment
rooms makes for a daunting maintenance program
in any conventional system. The requirements for
corrective and preventive maintenance are high and
access to the track is difficult; maintenance is
conducted during the wee hours of night when
the system is closed to passengers traffic.
Equipment in a CBTC system is significantly
lower and therefore the space required in the
equipment rooms and along the track is also
low. Resulting in a reduced maintenance
program (unless it’s a conventional system with
a CBTC overlay). More important, the need to
access the track is reduced.
Automatic Speed Regulation (Ride Quality) –
Uniform ride quality from one train to the next
is a staple of a CBTC system. A CBTC train will
travel at the same speed and brake at the same
rate at the same point on the track every time.
The acceleration and braking is gradual and jerk
is reduced or eliminated when departing or
arriving at a station. In a conventional system,
the passengers are left at the mercy of the
driver. The driver may accelerate suddenly or
brake hard, drive in excess or slower than the
posted speed. The ride quality will differ from
one driver to the next.
Bi-Directional Operations – A conventional
system is designed for maximum efficiency in
the normal running direction. Due to cost and
complexity, the reverse running direction is not
optimized and headways are large. Recovery
options in an emergency situation are also
limited. However, in a CBTC system there is no
concept of normal or reverse running; the
design is optimized for both directions. Only the
civil design of the track limits the efficiency of
the system (the placement and orientation of
cross overs and curves).
Reduced wear and tear of train propulsion and
braking system – A CBTC systems ability to
regulate speed and acceleration reduces the
stress placed on the braking and propulsion
unit when compared to a human driver in a
conventional system. A CBTC train operates
within the design limits of the braking and
propulsion unit maximizing its life while
reducing maintenance costs.
© METRO RAIL NEWS | OCTOBER 2017 | WWW.METRORAILNEWS.IN
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