EDINBURGH'S beleaguered tram system is expected to attract fewer than half of the number of passengers originally expected after its route was truncated to save money.

Secret forecasts drawn up for Edinburgh City Council predict 5.4 million people a year will use the service between the airport and St Andrew Square in the city centre when it opens in 2014.

That compares to a forecast of nearly 12 million passengers travelling each year on the full 11-mile route, including the section from the city centre to Leith and Newhaven Harbour that was mothballed last year.

The figures, disclosed to The Herald following a Freedom of Information request that was ultimately referred to Scotland's Information Commissioner, illustrate the long-term difficulties created by cutting off developments east of the city centre that the trams were to serve.

Even after nine years of operation, the curtailed service is expected to attract fewer than 10 million passengers, while the full route, known as 1a, would have attracted about twice that number.

Under the revised programme agreed last August, the council will have to find an additional £15 million a year for 30 years from its budget to fund loan repayments needed to complete the project, the costs of which have gone from £545m to £776m.

However, council officials have stressed that operating the trams will not have a negative impact on the public purse because, although there will be less revenue from passengers, operating costs for the shortened route will also be reduced.

In the first three years, the airport-to-St Andrew Square route is expected to lose nearly £5m before breaking even the following year, while the full route would have lost £700,000 more than this.

However, after nine years, the annual profits of the shorter route are significantly lower, at £1.4m – just over one- third of the £4.1m predicted for the full route.

Lothian Buses, the council-owned firm that is due to take over tram operations, is also expected to benefit financially from the shorter route as fewer of its own services will require to be withdrawn. Its profits, which have not been disclosed, will be used to subsidise the tram operation in the first three years.

Alan Coyle, the council's finance, commercial and legal manager, said the combined tram and bus operation would be profitable from the first year.

While standing by the patronage and financial forecasts, he claimed there was room for these to be improved under the revised management structure that will see control of the trams handed to Lothian Buses, instead of Transport Edinburgh Ltd (Tel), which was to operate both tram and bus services.

The forecasts for the airport-to-St Andrew Square route were originally drawn up in August 2010 as part of a refreshed business case for the tram project as the council contemplated shortening the route, but were revised slightly upwards last summer.

The 2010 modelling, undertaken by transport consultancy firms Steer Davies Gleave and Colin Buchanan, shows the impact the recession has had on the tram's business case as a slowdown in housebuilding and office developments led to 1.7 million fewer predicted passengers in the first year.

The Herald asked to see the passenger forecasts last September, but the request and a subsequent appeal were turned down by the council, which agreed to release the figures earlier this month after the case was referred to the Scotland's Information Commissioner.