THE revamp of Truro's Trafalgar Roundabout has cost taxpayers £1.2 million more than it should have, the West Briton can reveal.
Enlarging the roundabout to include a bus lane and traffic lights was meant to cost £2.25 million but the bill has now reached £3.43 million.
The development has been criticised for making traffic problems worse, with queues lengthening on all approaches.
The West Briton obtained the final cost for the 14-month project in a freedom of information request to Cornwall Council.
Told the figure, Rob Nolan, Cornwall Council member for Redannick, said: "That's shocking. We have terrible parking problems in Truro; people feel under siege in their own homes and I've asked for a solution based on yellow lines, residents' parking and lower car parking charges, but I'm told there's no money.
"Meanwhile millions of pounds are wasted on a scheme that kept residents awake at night while it was being built, has caused longer queues of traffic than we ever had and flooded at the first sign of rain."
Part of the increase in costs came from compensation paid by the council for hotel stays and triple-lined curtains for neighbouring residents.
Mr Nolan said: "The people responsible should never be let near a traffic scheme in Cornwall again."
The scheme has been introduced ahead of creation of the new park-and-ride at the top of Tregolls Road as part of the Waitrose development.
Kel Pritchard, who lives at Trafalgar Row, facing the roundabout, said: "The cost is quite frankly ridiculous.
"The traffic build-up is far worse than before with queues stretching further back and I've also noticed an increase in the tooting of horns."
Tim Wood, the council's assistant head of transport, said the roundabout carried more than 40,000 vehicles a day, with a network of pipes and cables beneath.
Although the council originally gave the £2.25 million figure, he said, the budget was now £2.53 million, which included £279,000 for diverting and replacing ageing pipelines for gas and water companies.
Mr Wood said the difference of 36 per cent was "due to the additional complexity and need for more temporary traffic management in lane closures and for pedestrian access over open trenches.
"Diverting the services for the utility companies involved significant lane closures to enable contractors to carry out pipe-laying without causing a risk to the travelling public.
"The nature of this work resulted in open trenches for long periods in the existing footways that required the installation, moving and dismantling of boardwalks necessary to maintain public access."
He added that steel plates were needed to cover open road crossings, and that doing work mainly at night to minimise disruption avoided daytime road closures which "would have cost the local economy around £80,000 each day."