THE northern French city of Lille was the birthplace of the VAL automatic rubber-tyred light metro, having been invented by Prof Robert Gabillard of Lille North University and developed by Matra (now part of Siemens) for the city's first metro line which opened 30 years ago in April 1983. The metro is now being upgraded to handle 52m-long trains, double the length of existing trains in a project that includes the first installation of Alstom's new CBTC system Urbalis Fluence.

Today, the Lille metro consists of two lines totalling 45km operated by a fleet of 143 trains with operating headways of just 1 minute. A year ago, Alstom was awarded a e250m contract to modernise the 13.5km Line 1, including the supply of 27 trains and resignalling the line while retaining the 1 minute headways. The new trains are expected to enter service in January 2016 with completion of the project scheduled for 2017.

Alstom started to develop its new CBTC system in 2010 following discussions with more than 30 customers in 15 countries to analyse their requirements and try to develop a product which differentiates itself from other CBTC systems on the market.

Lille-cbtcUp to now automatic train control (ATC) has always been overlaid on the traditional interlocking sub-system which increases complexity. In conventional CBTC systems, routes are secured by the interlocking. Whether it is a separate cubicle or integrated with the zone controller, the interlocking is functionally a dedicated sub-system. This implies complex interfaces between the interlocking, automatic train supervision (ATS), and the wayside and onboard ATC, in order to achieve the best performance and the shortest headways.

Alstom's research and development programme focused on a thorough examination of the existing Urbalis CBTC architecture to see whether it was possible to simplify it.

The research concluded that it is possible to integrate the routing and interlocking functions on the train and on the lineside object controllers, so that track resources such as points, flanking, overlap, and platform screen doors can be booked directly by the train to the object controllers, removing the traditional and unnecessary split into separate sub-systems, ie the ATC and interlocking. Another innovation is direct train-to-train communication, for simpler communication paths and shorter response times.


At the start of a train's service, or for any movement, the train receives its mission, such as the schedule or next station, from the ATS. As the track description is already embedded onboard the train as with any CBTC system, the train is able to identify all the track resources that it will need to perform its next movement. The train then asks the corresponding object controllers for these resources.

Each object controller responds to the train to confirm that the requested resources have been allocated and are locked, and if needed moves the points to the requested position. When resources have been booked and locked, the train can extend its movement authority and move. When the train has passed a track resource according to its own automatic train protection (ATP) primary detection, it immediately releases the resource which is then available for another train. As soon as a track resource is booked, and as long as it is not released, it cannot be used by another train, and all safety principles are enforced.

This new method of working makes train movement very flexible because the train can safely travel from its current position to any other location as there are no longer any traditional constraints from interlocking principles and the track becomes a commonplace. Other train movements are possible such as bi-directional or shuttle operation, and turn-back at an intermediate station or the end of the line. According to customer needs and practices, all operational principles can be implemented through an overlay of this core mechanism.

In conventional CBTC systems, trains regularly send their location report to a zone controller. After processing the reports, the zone controller sends back an end of authority to each train which enables the train to define its speed control curve. This implies periodic communication between onboard ATC and wayside ATC (zone controllers).

The moving block principle is retained with Urbalis Fluence, but there is direct communication between two consecutive trains to ensure the correct headway is maintained. The following train asks the preceding train for its position, and the preceding train sends back its current position, updating it regularly. This allows the following train to immediately update its speed control curve.

As there are fewer subsystems and interfaces, response times should be better leading to improved performance. Alstom estimates that Urbalis Fluence will result in a 20% reduction in lineside equipment and will be about 20% quicker to install because less engineering and configuration is required. Maintenance will also be simplified as the equipment will be installed on the trains rather than out on the track and so it can be attended to in the depot. As Urbalis Fluence is expected to be cheaper and simpler to implement and maintain than conventional CBTC, it should be a viable option for installation on monorails and automated light transit systems thereby expanding the market for CBTC.

Another important benefit is that there are no more inter-sector constraints. Line extensions can be equipped more easily, without impacting the vital data-preparation of existing sections.

Nevertheless, Alsom still sees a role for its conventional Urbalis 400 CBTC systems. "We will offer both systems because there will be some customers who want to retain their interlockings or who have mixed traffic operation, and particularly where a customer wants to extend an existing line," says Mr Pascal Clere, Alstom's senior vice-president for transport information solutions. "We will therefore continue to develop Urbalis 400."