How other cities do it
London
On most weekends, London Underground issues notice of track repairs, often closing a section of the network and rerouting trains around it. Special buses are laid on to ferry passengers between closed tube stations.
"These are planned a long time in advance, and a lot of time is taken to ensure proper notice is given," according to a spokeswoman. Engineering work is concentrated between 1 a.m. and 6 a.m. or at weekends.
"It would have to be very serious for us to close during the week. We would call that a major closure," she says.
Derailments on the Underground in January and October, injuring 32 people, have brought the issue into sharper focus.
London's Docklands Light Railway, which carries 44 million passengers a year (20 million more than the DART), says the nature of disruption depends on what engineering works are taking place - but track closures are known to happen. Last April, the company ran a station-enhancement scheme without closing platform facilities or stopping trains.
Joe Humphreys
Paris
On the Paris Metro system and the suburban RER (the equivalent of the DART), priority is given to passengers' convenience. The Parisian public transport authority, RATP, schedules maintenance work in the early hours or during summer holidays. The Metro is closed between 1 a.m. and 5 a.m. every day, which is when most work is carried out, despite higher labour costs.
"When we have to replace a railway line, including the ties and gravel beneath it, we may close a line from 9 p.m. until 5 a.m., but even then we operate normal hours on Friday and Saturday nights," says Michel Dubois of RATP.
For more extensive work, segments of track or stations are shut down during the month of August, when the number of passengers drops from 3.5 million to one million per day. Last summer, the viaduct between the Jaurès and Blanche stations in northern Paris, and the Musée d'Orsay RER station, were closed during August. RATP ran a free substitute bus to replace the closed segment of the RER line.
There are 200 Metro stations in Paris, and some are occasionally closed for refurbishment. The inconvenience to passengers is minimal because stations are, on average, only 500 metres apart and nearby stations are kept open.
RATP will complete a 30-year plan to renew 200 kilometres of track in 2010. "Most of the time," Dubois says, "passengers don't even realise the work is going on." - Lara Marlowe
New York
In the city that never sleeps, the same can be said of its 24-hour subway service. Even when line upgrades are done the New York City Transit Authority ensures that the work is done at night or during off-peak hours. When a section of the system is taken out to be rebuilt, there's always another track to fall back on - to allow for re-routing around any work area.
"In general, the system runs like clockwork," says Charles Seaton of the NYC Transit Authority.
It is impressive for a system of its size. Unlike Dublin, which has, essentially, one north-south line to worry about, New York has 26 lines carrying 4.6 million passengers a day. It's a remarkably effective transportation model, considering it's 100 years old next year. Seaton says New York just wouldn't function without its subway. The few times it has shut down - during a 1980s strike, after the 9/11 attacks, and during blackouts in 1977 and 2003 - the city has just stopped working. New York cannot afford even a day without its subway.
"That's why most of the work that's done is done keeping the system up and running," Seaton says. Whether it's four in the afternoon or four in the morning, in New York there's always another train on the way. - Ian Kilroy
Berlin
Berlin has a public transport system most major cities can only dream of. With nine underground lines, 14 suburban lines, 28 tram routes and 160 bus routes, regular maintenance work causes only minor disruption because commuters can always swap between the networks.
The underground (U-Bahn) network through the city first opened in 1902 and is now 150 kilometres long. Minor maintenance work is carried out on weekday nights when the U-Bahn stops running, between 1 a.m. and 4 a.m. When a short stretch of tunnel needs more extensive work, builders work on one track at a time. Commuters walk across the platform to continue their journey on a waiting train, which switches to its correct track after passing the stretch of track under construction.
At the moment, the 20-kilometre U5 line from the eastern suburbs into the city centre is under construction until the end of next year. Five-kilometre stretches of the line are closed for three months at a time to renovate stations and replace tracks and signalling systems. Buses wait for commuters disembarking from each train and carry them the five-kilometre stretch by road. Despite the inconvenience, surveys have shown that journey times have remained steady.
The city's suburban rail (S-Bahn) network, carries nearly 300 million people annually, more than a million people each working day. When major construction work takes place, which is quite often, and sections of the network are closed for three months at a time, the company provides replacement buses and still manages to achieve a punctuality rate of more than 95 per cent. - Derek Scally
Madrid
The Spanish capital has a population of five million, and almost a million of them use the Circanias commuter lines into the capital every working day. Demand has increased almost tenfold over the past decade as new dormitory suburbs have sprung up.
A spokeswoman for Spanish rail company RENFE confirms that most lines are two-way, and many are multiple as they approach the Atocha and Chamartin termini. She says: "When maintenance or modernisation work needs to be done, they try to plan it around low periods such as weekends or August when people are away. It is nearly always possible to switch the trains to other lines."
The Metro de Madrid dates back to 1919 when the first line was opened by King Alfonso XIII. It now consists of 12 lines and 190 stations, covering 227 kilometres. Last year 565 million passengers used the service, which has been modernised in recent years. One popular recent agreement made the €5.50 ticket for 10 rides valid for both Metro and buses. All trains are now fully air-conditioned and three new lines were inaugurated last year. A spokeswoman for the Metro says it does occasionally have to close a stretch of line for works, as was done recently when a new line under construction crossed with a line already operating.
"We had to close one station, but laid on free buses to take passengers to either of the two closest stations," she said. - Jane Walker