THE CBD Metro will run as much as 87 per cent empty during the height of the morning rush hour when it opens in 2015, the Transport Minister, David Campbell, has conceded.

Although the $5.3 billion metro between Central Station and Rozelle will have a capacity of 30,000 passengers an hour, as few as 4000 to 5500 passengers will use it, the Government estimates.

That means the equivalent of 26 of the 30 trains running each hour in the peak will be empty. Off-peak passenger loads are likely to be half again.

By contrast, 27,650 passengers travel along CityRail's western corridor to the city in the one-hour morning peak, which includes services from the west, inner-west and northern lines.

The figures, supplied by Mr Campbell's office, show most CBD Metro trains will be empty for decades. By 2031, just 7250 people an hour will travel on the CBD Metro in each direction according to the Government's forecast, which means it would be operating 76 per cent empty at the busiest time of day.