Learn Discuss Railtex Network
11th
Communications systems for safety benefits Media Partners T
he demand for environmentally friendly mass transit systems becomes stronger as the population and size of
cities increase. For maximising rail capacity, increasing the number of trains is one part of the answer, but developing a signalling system to a new state of the art is another, and more critical issue. Communications based train
control (CBTC) is a railway signalling system that uses communications between train and track equipment to increase capacity by safely reducing the time interval (headway) between trains. By adding modern communication technology to previous automatic train control concepts, a CBTC system gives the position of a train with the maximum accuracy, and opens the track to a more efficient and safe way to manage railway traffic.
‘Based on the IEEE 1474 standard, the
CBTC system is now recognised as a ‘must have’ for all new metro line projects,’ says Thevenet.
Background Historically, traditional signalling systems have been based on locating trains in sections of the track called ‘blocks’. Each block is protected by signalling systems to prevent a train entering an occupied block. Since every block is fixed by the infrastructure, these systems are referred to as fixed block systems. The CBTC system introduces the concept
of moving block whereby the protected section for each train is no longer defined by the infrastructure. The trains are continuously communicating their position and status to the equipment in the track via a bi-directional link. This status includes, among other parameters, the exact position, speed, travel direction and braking distance of the trains, which continuously receive information regarding the distance to the preceding train and are then able to adjust their safety distance accordingly. In the late 1990’s, many projects emerged
and started to define the concept of CBTC. These were initially based on inductive loops, but the advent of digital radio communication technology was key in the development of the CBTC system. ‘One of the first CBTC projects
implemented on a large scale was the Paris metro line 14 which opened in 1998, and became fully automated in 2011. This system delivers an 85 second headway between metro trains,’ says Thevenet. ‘This can be considered as a major event in the development and interest in CBTC systems for cities. The
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Paris line 14 has shown that a metro can be operated fully unattended with greater train availability than any other line in Paris.’
Unattended train operation CBTC is now becoming a critical element of modern train operation. New metros all around the world now rely on CBTC systems to assist train operations from standard operation to fully automated unattended operation where trains can be operated from remote control centres without any driver on board. ‘CBTC systems cannot be discussed
without introducing what are the different train operations that are possible for modern trains and metros,’ says Thevenet. These generally comprise four elements: train movement, station stop, door closing and failure recovery. Looking at these areas in more detail it can be seen that: Train movement: passengers expect the train
to move from one station to the next. This is the most obvious element. This includes all operations that permit controls to accelerate and decelerate the train, including switching on the drive units. Station stop: accelerating a train is one
thing; decelerating it and stopping it with the right timing is another, involving not only precision and accuracy, but also the comfort of the passengers. Door closing: after the passengers have
exited or entered the train the doors will be closed. Again, there is nothing taken for granted in this operation, since this includes making sure no passenger will be blocked or
hurt by the doors. For train operators blocked doors are the main cause of delay in train movements. A standard time for door opening is 45 seconds, and any passenger blocking the doors generates a delay. Failure recovery: the volume of on board
equipment is increasing with the number of options and services available on trains. Any integrated equipment may be a possible cause of failure for the entire system, and the consequences of any failure must be addressed quickly and with the right decision in order to maintain safety. The above four elements can be used to
define train operations depending on who is performing the operation on board. Each of the elements can be performed
by a driver on board the train, not performed but attended to by a driver on board, or fully automated. The grades of automation are usually referred to as a GoA level: • GoA1 is conventional manual operation mode
• GoA2 is semi-automated operation mode (Semi automated Train Operation, STO)
• GoA3 is driverless operation mode (Driverless Train Operation, DTO)
• GoA4 is fully automated operation mode (Unattended Train Operation, UTO).
Safety and performance levels The higher the GoA level is, the higher the safety, functionality and performance levels must be. What makes CBTC systems unique is
the fact that they can be used in different operation modes. Trains equipped with a
Harness the power of interaction
Romaric Thevenet, marketing and technical support at Harting Technology describes a new intercommunicating system developed to increase the safety and frequency of trains on metro and suburban lines
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