Alistair Darling will today announce a £145 million scheme to reduce congestion at 92 traffic hotspots around the country.

Speaking at a seminar on private investment in the railways yesterday, the transport secretary warned that trains have a limited role to play in cutting congestion because of high costs and delays before extra capacity comes online.

He said: "We need to ask whether light rail or a bus-based solution is better. You can often get more for the same money with more flexibility and quicker results."

The Strategic Rail Authority has indicated that taxpayers may have to underwrite most of the planned £30 billion of private investment in the railways - a move which the Guardian blames on the Treasury's reluctance to back the scheme.

The newspaper reports that the Treasury has "put the brake" on plans for a £30 billion bond to fund the renewal of the rail network.