The Aberdeen Western Peripheral Route (AWPR) had previously been predicted as costing £347m, but delays and inflation have caused that estimate to rise dramatically.
The 28-mile-road was given the go-ahead by ministers in 2009, but various delays, including legal action by opposition campaigners, have caused the increase.
Transport Minister Keith Brown said the £374m estimate was made in 2008 and based on 2003 prices.
The Minister put the blame on "scope changes, the inclusion of standard risk costs and rebasing to 2012 prices."
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He said inflation had been responsible for a £230m increase in the cost.
Minister Brown was responding to a parliamentary question from Aberdeen Central SNP MSP Kevin Stewart. Mr Stewart has focussed the blame very much so on protester William Walton, who leads the group RoadSense.
RoadSense were responsible for mounting legal challenges to the decision to build the AWPR.
"People in the North East and across Scotland should be in no doubt that William Walton is the £230 million man," he said.
"These figures show just how heavy a price William Walton and RoadSense have imposed on people in the North East. Not only has an essential piece of infrastructure been delayed unnecessarily, but inflation has driven up costs while RoadSense had their repeated days in court."
Another development to make the A90 a dual carriageway between Balmedie and Tipperty is also expected to amount to £92m in costs. This brings the total for the combined project to £745m.
(IT)
