Ministers have given the final go-ahead to the extension of the M74 through south Glasgow and South Lanarkshire with the awarding of a £445m contract.
Transport Minister Stewart Stevenson approved the tender from the sole bidder, Interlink M74 - a consortium of construction companies.
Campaigners against the link said the tender was against competition rules.
Mr Stevenson said procurement was robust. Work is expected to begin in May and end in 2011.
The Scottish Government said the scheme would reduce congestion and provide links to regeneration projects in the east end of Glasgow.
Mr Stevenson said: "This project is also a crucial piece of the infrastructure which is required to provide excellent transport facilities for the visitors and athletes expected in the city as a result of the 2014 Commonwealth Games," he said.
Glasgow City Council leader Steven Purcell said the scheme was tremendous news.
The contract for £445m - plus an allowance of £12m for the possible treatment of mine workings - was awarded to a consortium which brought together Morgan Est, Balfour Beatty, Morrisons and McAlpines.
The Scottish Green Party said it was in breach of European competition rules.
One of its members lodged a complaint with the European Commission.
Glasgow Green MSP Patrick Harvie said the decision marked a "dark day" for the city.
"A sham tender process has been concluded with a sham review and an entirely irresponsible decision, given that the European Commission may pull the plug on the process altogether," he said.
Mr Stevenson said: "Following an internal review of the procurement processes the government is confident that the procedures are robust and we are happy for Glasgow City Council to award the contract to the Interlink M74 Joint Venture."
The five-mile extension is designed to connect the M74 to the M8, west of the Kingston Bridge in Glasgow.
Business leaders said the route would bring "significant economic benefits" to Glasgow.
Environmental campaigners said they were deeply disappointed by the decision.
Dr Dan Barlow, acting director of WWF Scotland, said: "At a time when we really need to see concerted and joined-up action by government to reduce our climate emissions, the last thing we need is yet another road building project."
The project had been backed by the Scottish Executive despite being rejected by a planning reporter after a public inquiry.