Fabrizio Cuppini Technical Manager ECM SpA
ITALIAN infrastructure manager RFI decided in 2006 to install automatic train protection across its entire network, following a series of safety-related incidents.
Most trunk routes and urban lines had already been fitted with the domestic SCMT system, whilst new high speed lines and international corridors are getting ERTMS. But this left around 5 700 km of secondary and regional lines which were not equipped with anything. An economical and effective ATP system was needed for these routes, where the maximum speed does not exceed 150 km/h.
Known as SSC (Sistema di Supporto alla Condotta, or Driver Support System), the equipment was approved for installation in April 2006. By the end of that year, more than 1 150 route-km had been fitted and a further 3 700 route-km was equipped during 2007.
SSC is intended to be complementary to ERTMS. Its simplicity can be attributed to the use of proven components, easy installation and minimal maintenance. It comprises trackside and trainborne sub-systems (SST and SSB), which communicate by a 5·8 GHz microwave radio using a secure protocol.
Lineside information points
Each trackside Information Point (PI) has an encoder and transponder, and is usually located close to an existing lineside signal. SSC can work with conventional lamps, dichroic mirror or LED signals. The signal aspects are identified and transmitted to the train as part of a structured data telegram which also contains information about permissible line speeds, braking rates and the distance to the next PI.
To minimise cost and simplify installation, each SST is powered from the signal to which it is connected. As a result, the unit must not draw more than 20 W. To meet Safety Integrity Level 4, it was essential that the SST should not affect the performance of the signal, for example by reducing the brightness of the aspect, or powering lamps that should be extinguished.
A pair of microprocessors in the encoder operate in a two-from-two fail-safe architecture to process data about the current state of the signalling, and prepare a data telegram which is modulated by the transponder and transmitted to the trainborne equipment.
The transmission is discontinuous, and only takes place as a train passes a PI.
The PIs along a route are linked by a chain of 'appointments', so that the trainborne unit can detect any PI which is not transmitting. At the entry to each SSC-equipped route, the appointment chain is initialised using a modified PI known as a data tag.
Taking the signalling data and the power supply from the local signal avoids the need for secure cabling or power feeds along the whole route. It also makes SSC compatible with almost any form of interlocking, potentially allowing the system to be used anywhere in Italy or even elsewhere in Europe.
The trainborne SSB provides continuous speed monitoring, using a speed profile which is calculated from pre-set train performance data and route-specific information received from the trackside.
Each trainset is provided with four antennae, on the left and right at each end of the train. GPS location equipment is also fitted, along with driver-machine interface displays in each cab. Once again, the SSB is designed to SIL4, with a fail-safe digital processor architecture.
Information from the SSTs is picked up by the antennae, and forwarded to a receiver unit which verifies that any telegrams are accurate before passing it to the processor.
The left and right antennae work with different frequencies (10·7 and 13 MHz) relative to the direction of travel. Thus the SSB can identify which PI is transmitting, and if this does not correspond with what is expected the emergency braking will be triggered.
The trainborne digital processor is the core of SSC. By combining signalling and route data from the incoming telegrams, with odometric information from the tachograph and GPS location system, it calculates in real time a safe performance curve, relays information to the driver, and operates emergency braking if the train exceeds speed limits because of operator negligence or other on-board problems.
Three separate speed profiles are generated as a function of the existing train position, and the lowest of these is taken as the reference speed.
A diagnostic system within the digital processor manages the Train Trip function and monitors the appointment chain. It will also halt the train if a stop signal has been passed.
If the SSB detects that a PI is not transmitting, the on-board processor operates the emergency braking system and localises the fault. The appointment chain is re-initialised automatically by looking up the distance to the next PI and calculating the distance covered using the odometer and GPS location data.
ECM is also developing a trainborne SSB sub-system which can interract with both SSC and SCMT, the conventional Italian automatic train protection system.
The Continual Signal Repetition codes transmitted via track circuits can also be read by SSB. Each train is provided with two pairs of antennae (known as 'captors') placed before the leading wheelset at each end of the train.
The SSB sub-system also has one or two dedicated antennae (depending on the train length) placed beneath the vehicle to communicate with SCMT Eurobalises at a frequency of 27 MHz.
An on-board digital processor can detect which system is transmitting data signals and manages their implementation. A touch-screen display in the cab enables the driver to monitor whichever system is in use at a given time, allowing an SSB-equipped train to operate with both SSC and SCMT train control systems.
- CAPTION: RFI is currently fitting a large portion of its regional network with SSC, a low-cost form of automatic train protection. In the region around Bari, 545 km of secondary lines were equipped in 2007
Installation status of SSC as at December 20 2007
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