The upgrade work, which was given the go-ahead in December 2010, includes the six-mile "missing link" on the M8 in North Lanarkshire.
Improvements to the Raith Interchange and widening of key sections of the M8, M73 and M74 are part of the plan.
Construction work is due to start next year and is expected to be completed by 2017.
The full cost of the project, which includes utility diversions, design preparation, land purchase costs and inflation since 2007, will be £508m.
The cost is much higher than previous estimates of £320m but Transport Scotland insisted the programme was more ambitious than previously announced.
It includes the upgrading of the A8 between Baillieston and Newhouse to motorway standard.
This will require upgrades to the connections to the M73 motorway at Baillieston and a new junction at Shawhead, which will connect to the A725 East Kilbride road.
There will also be new junctions at Eurocentral and Chapelhall.
Improvements to the Raith Interchange near Hamilton in Lanarkshire include realignment of the A725.
There will be an underpass for the A725 and bridges carrying the Raith roundabout.
Scottish Transport Minister Keith Brown said the project was of a similar scale to the recent M74 completion which directly supported 900 construction jobs.
He said the improvement were expected to cut up to 18 minutes off the journey time for about 115,000 vehicles for the busiest sections of the M8.
Mr Brown said: "The Scottish government's spending on infrastructure projects is a key driver in boosting the country's economy.
"In these difficult economic times providing hundreds of jobs in the hard-pressed construction industry plays a key part in delivering our vision of a wealthier, fairer and better connected Scotland."
Scottish Green MSP Patrick Harvie said: "The spiralling cost of the SNP's obsession with motorways isn't doing Scotland any favours.
"Last year the M8/M73/M74 upgrade was valued at £320m - now we learn it's going to cost us over half a billion.
"And that cost doesn't include the lifelong maintenance that will be heaped upon us too."
He added: "These projects will benefit those who can afford to drive and will do nothing to reduce inequality, air pollution and greenhouse gas emissions."
Plans to upgrade the motorway network in central Scotland will cost £415m, the Scottish government has announced.