A high court judge is deliberating after a legal challenge to the Heysham to M6 link road.
A two-day hearing in Manchester on Tuesday and Wednesday saw campaigners contest the decision to rubber-stamp the £123m road.
Lancashire County Council said the legal action by Transport Solutions for Lancaster and Morecambe (TSLM) had delayed starting work on the road and could increase the cost of the scheme.
David Gate from TSLM said: “We are quite encouraged, the judge is clearly giving things serious consideration.”
Mr Gate said the decision was being challenged on legal grounds.
TSLM claims the road is not a nationally significant infrastructure project, the public consultation into the road was inadequate, that the examiner relied on national policy statements on building roads near power stations but Heysham 3 may not be built until around 2030, and that the presence of otters at Halton, which may be affected by the road, was wrongly disproved.
The judge’s decision will be sent to the Department for Transport, Lancashire County Council and TSLM. There is no indication of a timescale.
The road was granted final permission by Transport Secretary Patrick McLoughlin in March. Building work was due to start this summer.
County Coun John Fillis, cabinet member for highways and transport, said: “Our legal team made a strong case rejecting the five grounds put forward by the objectors against the decision by the Secretary of State to award planning permission to the scheme.
“On conclusion of the two day hearing the judge decided to issue a written decision. We are now waiting for the decision to be made available.
“The hearing has delayed construction, this has added a further £600,000 to the preparation side of the budget.
“The £470,000 increase in the construction costs has been kept within the budget due to contingencies that were built within the budget when it was prepared.
“However, this is still an extra cost to the county council which otherwise could have been a saving.
“The scheme will still provide excellent value for money in terms of the considerable benefits for local businesses and employment while acting as a catalyst for wider economic growth.”