The state railway company has also asked potential suppliers to propose vehicles which use green technology such as hybrid power and regenerative braking to reduce their energy consumption.

The majority of the new 400 carriage order will be for 250 DART carriages to cater for the company's plans to extend the service to Maynooth and Hazelhatch and to Balbriggan in Co Dublin.

The carriages will also service the company's proposed new 1.3bn underground interconnector line in Dublin, which will link the city's rail lines.

The remainder of the order will be for 150 dieselpowered commuter railcars, which will be used to expand commuter services in Cork and Limerick as well as cater for the planned reopening of the Cork to Midleton railway line and the first phase of the Western Rail Corridor.

The order is also likely to safeguard the future of the lightly-used branch line between Limerick and Ballybrophy in Co Laois, which had been threatened with closure, as the company intends to use some of the new carriages on that route.

It is unclear, however, what the company's plans are for the other route threatened with closure at that time, the line between Rosslare in Co Wexford and Limerick Junction.

The company plans to place the order in two phases with the majority of the carriages being ordered later this year with a further order in 2011.

However, a spokesman said that this depended on the scheduling of its expansion plans.

"We are examining the best phasing of electrification and resignalling work to ensure that we can deliver capacity improvements to commuters, and optimise value for money for taxpayers in our investment programme, " he said.

A number of the world's leading carriage makers are expected to tender for the orders with the early favourites being Spanish group CAF, which won the company's most recent commuter railcar order, and Japanese supplier Mitsui, which is currently supplying it with new intercity railcars, which are due to enter service later this year.