Transport Scotland has formally started the bid race to build the Aberdeen Western Peripheral Route.
The big bypass project will now be bundled together with the £100m Balmedie to Tipperty road scheme and will be let as a single contract worth between £472m and £506m.
This estimate depends on whether a third River Don crossing is included within the scope of the contract.
Transport Scotland bosses hope to select four bidders to tender for the major road project after the prequalification round.
A winner for the Non-Profit Distribution (NPD) contract will be announced in August this year to complete the road by the spring of 2018.
A second part of the tender includes maintaining the 46 km dual two lane road over 30 years.
Interested firms have until 4 March to complete prequal documents, which can be found at the Public Contracts Scotland web site.
More than 150 delegates representing 60 firms have already attended the prospective bidders day earlier this month.