Minister for Transport Martin Cullen turned the sod on the first phase of the upgrade of the M50 motorway this afternoon.
During the first phase, a third lane will be added to the 5 kilometre section of motorway between the N4 and the Ballymount interchanges, which will also be improved.
In the second phase, another 31 kilometres of motorway between the M1 and Sandyford, will also get a third lane.
The Westlink toll plaza will also be upgraded to a fully electronic free-flow toll plaza.
According to the National Roads Authority (NRA), the upgrades, which will cost around €810 million, will increase the M50's capacity to 180,000 vehicles.
Widening the motorway and upgrading 10 of the access points along the route is intended to reduce the average travel time by 19 per cent in 2008 and 11 per cent in 2023. The M50 has cost more than €1 billion over 20 years to build.
"The move from four to six lanes, plus free flowing interchanges will improve average peak hour speeds, reduce traffic congestion on the radial routes and improve traffic flow on the whole of the Dublin road network," Mr Cullen said.
Fine Gael's transport spokeswoman Olivia Mitchell said the M50 upgrade will mean years of disruption for Dublin's beleaguered motorists. "The NRA's best estimate is that the entire project will take at least seven years, and realistically will take ten years," she said.
Mr Cullen said the concerns of residents were understandable, but pointed out there was a clause in the upgrade contract requiring the contractor to maintain traffic flow during works.
He also announced a M50 Upgrade Traffic Group will oversee traffic management arrangements. This group is be made up of representatives of the NRA, local authorities and the Garda.
Last weekend, it emerged the NRA intends to replace the Westlink toll bridge with barrier-free electronic tolling by 2008. Under the plans, the State will buy out the right of National Toll Roads (NTR) to operate a toll plaza on the road, in a compensation package that will be worth about €500 million to the company between 2008 and 2020.
The NRA will respect the terms of its contract with NTR, which runs up to 2020. NTR will be paid a share of the toll revenue based on 2007 levels, with inflation also taken into account.
Ms Mitchell accused Mr Cullen of entering a "sweetheart deal" with the NTR that offers "appalling value" to taxpayers.
"Taxpayers will be paying out €1 million a week in order to buy the Westlink toll bridge back from NTR, when they have already paid for it many times over," she said. "The whole shambles is a monument to bad planning and bad management."
