Iarnrod Eireann expects to lodge its planning application for its £50 million (€63.5m) redevelopment of Tara Street DART station in Dublin this week.

The development is notable not only because it is the second time that the company has effectively sold the air over its properties, but also because physical restrictions at Tara Street are holding up investment in suburban rail of almost £400 million (€508m). This investment will almost double the capacity of the Capital's suburban rail network.

With so much riding on the outcome of the planning application, Iarnrod Eireann personnel are keeping their fingers crossed that An Bord Pleanala - which will undoubtedly be the final adjudicator - will see the project as a significant element of state infrastructure.

Essentially, the redevelopment comprises office accommodation over 14,580 sq m in a tower-like structure which is to be higher than Liberty Hall across the river, with a roof restaurant, a bar and a terrace amounting to 1,184 sq m. There will also be a basement on two levels with 52 car spaces comprising 3,120 sq m.

With the new development, Iarnrod Eireann has an opportunity to create a new landmark which could create a new symbol for the city to rival the spike proposed for O'Connell Street. The move to realise the potential of the space above the station follows the very successful similar move which financed the revamp of Connolly Station some years ago.

Tara Street Station is even more important in suburban terms than Connolly. It is the busiest station in the entire rail network, handling 25,000 people per day or seven million passengers per year. Since the introduction of the DART system more than 20 years ago, there has been steady and sustained growth in passenger numbers, but the proposed development would provide a station which would be capable of handling up to 60,000 passengers per day or 17 million passengers annually.

Iarnrod Eireann says the station would have the capacity of handling up to 14,000 passengers per hour at peak times. Crucially, it will extend the platforms to 168 metres which will allow six and eight-carriage trains in a move which will have the desired effect of radically increasing the number of passengers per hour through the central corridor. It is intended that the station will service as an interchange with the metro when it is built. The sale of the air rights will make the redevelopment of the station self-financing for Iarnrod Eireann.

For the customers there will be a new station concourse with access off Tara Street and Georges Quay. The new concourse will include ticket sales and a retail area and will have a ground floor area of 2,400 sq m. The concourse will be 13 metres high (42 feet) giving good visibility of the trains from ground floor.

The entrance from Tara Street will be set back 6 metres from the existing pavement edge to give widened pavements. Widened stairs and escalators will take passengers to the overhead platforms which are to be partially covered by a glass roof.

At the southern end of the platforms a new station exit will be provided adjoining the new Ulster Bank development presently under construction.

The metro interchange station will be below street level.