WHEN the tunnels for the North West Rail Link are finished in just over four years, they will have an internal diameter of about 6.1 metres, too small for the type of trains used in Sydney.
The Transport Minister, Gladys Berejiklian, said the decision to bore smaller tunnels for Sydney’s biggest rail project in decades was not about saving money.
But the commitment to smaller tunnels has sparked fears among some transport planners that, for the sake of a few centimetres on either side, the government could be forever locking off transport options.
This is because the size of the tunnels may not affect only the type of trains that use the North West Rail Link.
The government has also committed to connecting the north west link with another rail crossing for Sydney Harbour, so it will also have implications for the types of trains that use that crossing.
One concern is that it could limit the harbour crossing’s ability to accommodate double-deck inter-urban trains, or even highspeed trains if they were introduced on the east coast.
The project director for the North West Rail Link, Rodd Staples, told an industry briefing last week the tunnels would have an internal diameter of 6.1 metres.
This is about 40 centimetres smaller than tunnels bored for the Epping to Chatswood link.
It is also too small to fit a Sydney double-deck train and its overhead wiring, according to the government and several rail industry sources.
The trains are about 4.4 metres high and are powered by overhead wiring, which on RailCorp’s guidelines, has to sit more than six metres above the rail.
One consultant who attended last week’s industry briefing said if the North West Rail Link was built only for single-deck trains, it would be ‘‘almost inevitable’’ the second rail crossing would be limited to similar trains.
Another planner said it was crucial the second crossing allow express services from the central coast or Newcastle, using doubledeck trains, or high-speed rail.
‘‘The basic question is are we thinking about the Sydney basin, or also areas beyond the Sydney basin? If we are going to be spending so much money [on another harbour crossing] we should be,’’ the planner said.
On the government’s timeline, the contract for tunnelling the twin 15.5 kilometres underground for the North West Rail Link will be signed in about a year.
This will allow the four tunnel boring machines it is ordering to be in the ground by the middle of 2014.
The chief executive of industry group the Tourism and Transport Forum, John Lee, said it was conventional to shape the size of a tunnel around the type of train to run through it.
‘‘I think it has been a smart decision,’’ Mr Lee said.
Ms Berejiklian said: “There will be some cost savings in building smaller tunnels, however, there will also be some additional costs like the conversion of the Epping to Chatswood rail tunnels to this new rapid transit system.’’
“The second harbour crossing will be part of the rapid transit network.
Fast, high-capacity, single-deck trains means we can move more people every hour than regular double-deck services.’’
However, the Herald’s transport inquiry of 2009 and 2010 argued against this analysis and found that double-deck trains could carry more people.