The reasons why and some of the issues surrounding CBTC were debated at last November's Global Transport Forum conference on CBTC, as David Briginshaw reports from Amsterdam.

INCREASING demand for urban rail is spurring the construction of new lines and putting many existing metros and commuter rail operations under growing strain. But building new underground lines is very costly. Similarly upgrading existing underground lines by extending station platforms to allow the operation of longer trains is prohibitively expensive and disruptive and in most cases out of the question.

For new projects, the goal should be to develop solutions that optimise the capacity of costly infrastructure, while for existing lines the objective should be to get more out of what has already been built. These twin objectives help to explain why more and more operators are turning to Communications-Based Train Control (CBTC) with its ability to provide headways of less than 90 seconds while maximising the flexibility in the way the line is operated.

Sao-Paulo-CPTMCBTC permits a reduction in capital and operating costs because short headways allow high capacity to be achieved with short trains and station platforms, while automatic driverless operation means fewer staff are needed. Mr Thierry Bonnefous, urban solutions director with Alstom, explained that conversion of metro Line 1 in Milan to CBTC operation has increased capacity by 20% with the same length trains running more frequently which has boosted both ridership and revenue.

Mr Dan Filip, director of business development and transportation solutions with Thales, revealed that introduction of CBTC on the Muni Metro LRT network in San Francisco increased capacity sufficiently to avert the need for a new line, while in Mecca, Saudi Arabia, CBTC avoided the necessity for 36-car trains and exceptionally long platforms to move the vast numbers of pilgrims between religious sites, by permitting a more flexible operation using convoys of three 12-car trains running at 90-second headways, giving a capacity of 72,000 passengers/hour/direction.

The benefits of fully-automatic driverless operation are already apparent in Singapore where the North East, Downtown and Circle lines have been equipped with CBTC from the outset. Singapore Mass Rapid Transit (SMRT) is now in the process of equipping its original metro with CBTC using Thales Seltrac with moving block and bi-directional operation at a cost of €300m.

Mr Khoo Hean Siang, SMRT's executive vice-president, trains, says 90-second headways will increase capacity by 20%, but he also expects the new system to improve reliability, not only because the old signalling system has become increasing unreliable. "Most of the problems we have are caused by drivers making mistakes - a driverless system is three times more reliable than a manually-operated one," Khoo said. "We also have a 30% attrition rate for train drivers, so we constantly have to recruit and train more staff." The only downside is that SMRT expects the cost of maintaining the CBTC system will be slightly higher than for the existing signalling.

SMRT has set a five-year timetable to complete the project which will be implemented in phases. Trains will be dual fitted with both signalling systems to facilitate the switch-over which will start with shadow CBTC operation. The legacy signalling will be retained for a while as a fall-back while the new system beds in, before eventually being removed.

Some operators are more cautious than SMRT and elect to retain their legacy signalling after CBTC has been installed. There are occasions when this is justified such as on complex networks where not all trains are equipped with CBTC or to avoid installing CBTC on maintenance trains and vehicles. Traditional track circuits are also useful for detecting broken rails. However, Mr Antonio Muñoz from Bombardier, believes most operators should be able to remove their legacy signalling equipment.

"Fall-back systems are not intrinsically needed for CBTC," Muñoz said. "In the long run they can degrade overall availability if they are not maintained properly and eventually become obsolete. If the fall-back system is hardly ever used, it probably won't work when it is needed." Muñoz says it would be far better to divert the money earmarked to maintain the fall-back system to improve the reliability of the CBTC equipment.

Mr D D Pahuja, director, rolling stock, signalling and electrical with Bangalore Metro Rail Corporation, disagrees with Muñoz. Bangalore will install CBTC on the two new lines it plans to build. "We need a fall-back system even if the CBTC fails only once," Pahuja told delegates. "A failure is a failure and we quickly get a huge amount of bad publicity, wasting all our good work. Signalling and telecoms only represents 5% of the capital cost of a new line. A fall-back signalling system may increase this to 5.5%, so it is worth it. It is similar to having a fire protection system, you must maintain it, train the staff to use it, and conduct drills."

Another subject under discussion in Amsterdam was interoperability. Mr George Hacken, senior director, vital systems with New York City Transit (NYCT), called for vendor neutrality so that equipment supplied by one company will work with equipment installed by another to achieve interoperability both within a CBTC system and between that and other equipment such as solid-state interlockings.

Mr Firth Whitwam, director systems architecture with Thales, told me that the push for interoperability should really come from the operators who need to tell suppliers exactly what they want. "The problem comes when operators go for the lowest price," Whitwam said. "All ideas of interoperability go out of the window as contractors strip out costs from their bids."

A relatively recent development is the use of CBTC and ETCS on the same line, as commuter rail operators look to CBTC to provide them with the throughput they need on the busiest section of the route which ETCS is unable to deliver. The £15.9bn Crossrail project in London is a good example. The core section of the line must be able to handle 24 trains/hour during peak periods and 30 trains/hour in perturbed operation. This section will be equipped with CBTC to provide automatic train operation with platform screen doors.

However, it will interface with traditional lineside signalling and ATP to the west of Paddington until the line is equipped with ETCS Level 2, and with conventional signalling to the east of Stratford until ETCS Level 2 arrives in 2025.

But there is another complication. The European Commission (EC) has deemed that Crossrail will be an interoperable railway, even though there will be no spare capacity for other operators, and therefore should be equipped with ETCS. As ETCS Level 2 cannot provide the capacity required, Crossrail has obtained derogation from the EC to install CBTC, with the caveat that Crossrail switches to ETCS Level 3 at some point in the future. But this is a long way off, as the development of Level 3 up to now has focused on providing a low-cost solution for rural railways.

Mr Duncan Cross, deputy director operations, London Overground, with Transport for London, fears that when Level 3 is developed for high-capacity metros, Crossrail could be the first line to adopt it with all the risks inherent in introducing a brand new system on what will by then be a very busy railway.

A similar situation is emerging in Paris. RER Line E will be extended west from its current terminus at Haussmann-St Lazare to La Défense where it will connect with existing lines to convert into a cross-city line. Line E currently uses a conventional signalling system which can cope with a maximum of 16 trains/hour, but when the line is extended the core section will need to cope with 22 trains/hour initially using a mixture of old and new trains and 28 trains/hour with only new trains. French Rail Network (RFF) recognises that only CBTC can provide this with ATO, even though it plans to install ETCS Level 1 on the outer extremities of Line E.

In addition to London and Paris, Istanbul is installing both CBTC and ETCS in the Bosphorus rail link and CPTM in São Paulo is fitting CBTC to three of its commuter rail lines. CBTC is clearly starting to gain wider acceptance by mainline railways, and this trend will continue until there is a viable alternative for providing short headways on busy lines.