The new section of the M74 motorway, which stretches from the Fullarton Road junction to the M8 motorway west of the Kingston Bridge on the south side of Glasgow, was opened to traffic on Tuesday.
The "largest ground infrastructure project" in Scotland was completed eight months earlier than expected.
Commercial vehicle drivers with van insurance cover can hope to enjoy shorter driving times in the area thanks to the early finish.
Infrastructure secretary Alex Neil said the project carried out by Transport Scotland delivered savings for the taxpayer as it was completed between £15 and £20 million under budget.
Mr Neil said: "This will mean significant savings for Scottish taxpayers and that drivers will be able to enjoy the benefits of this crucial piece of infrastructure several months ahead of schedule."
But Stan Blackley, chief executive of Friends of the Earth Scotland, said: "Half of all households in Glasgow do not have access to a car, so this new road will do little or nothing to help them. Instead, it will increase air pollution and carbon emissions - the project's own environmental statement confirms this."
© Press Association 2011