The opening of the Aberdeen Western Peripheral Route (AWPR) is expected to be delayed until late autumn, the Economy Secretary has said.
The Scottish Government had hoped the £745 million project would be completed by the spring following previous setbacks.
However, Keith Brown told MSPs the further delay had been caused by adverse weather, contractor disputes and the collapse of construction giant Carillion.
Carillion formed part of the Aberdeen Roads Ltd (ARL) consortium, leading the work alongside Balfour Beatty and Galliford Try.
Mr Brown said that although ARL has said its target is to open the 28-mile bypass during August, Transport Scotland has indicated a "late autumn" completion is anticipated.
"The contractor has cited delays which it attributes to factors including the cumulative effects of weather events on the project such as Storm Frank in 2015 and delays in relation to the timing of public utility diversions," Mr Brown said.
"An additional complicating factor has arise from the collapse of Carillion, one of the joint venture partners."
Mr Brown said he had been advised by Transport Scotland that an August opening was "based on somewhat aggressive programming with limited contingency".
"Whilst I welcome the efforts being made by the contractor to secure as early an opening as possible, I've been advised that it's prudent to anticipate the potential for a late autumn 2018 opening date for all project roads."
Conservative MSP Dean Lockhart said: "The announcement of yet another delay to the AWPR will come as a massive disappointment to the people of the north-east.
"This is a project that has already been significantly delayed."
Labour MSP Lewis Macdonald called on the Economy Secretary to "deliver some absolute certainty to people in the north-east as to when this road will be finished".
Liberal Democrat MSP Mike Rumbles branded the timescale a "complete shambles".