Shropshire Council said that people now have until May 7 – next Friday – to respond to the proposals for the North West Relief Road around Shrewsbury.
The council said that no date has yet been set for when a decision will be taken on the £87 million plan, but added that it expected it to be "later this year".
There have been around 2,000 responses to the application so far, with campaigners against the proposal suggesting there could be as many as 3,000 objections when all submissions are counted up.
Protesters have also held demonstrations outside the council's base at Shirehall and on land where the road would be built.
Among the latest people to formally object was Oswestry Town Council, which described the scheme as a "waste of taxpayers' money".
If approved the four-mile road would stretch from Churncote Roundabout to Battlefield and would effectively complete a ring-road around Shrewsbury. The new section will be single carriageway.
Ian Kilby, planning services manager at the council said the extension had been agreed because of the importance of the proposal.
He said: "Due to the significance of the Shrewsbury North West Relief Road planning application to the local community, we have extended the consultation period from the statutory 30 days to 56 days to allow more time for people to consider the proposal and submit their comments.
“Consultation on planning applications can include a range of methods including email, letter and site notices. It is typical for the site notice to be displayed on a date following the other methods of notification as part of the planning officers site assessment, so the 56 day date in this case will correspond with the display of the site notices which is May 7."
Mr Kilby said that despite the deadline, comments received after May 7 could be taken into account.
He said: “Planning applications are time sensitive and there are defined periods for determination which can be extended by agreement with the applicant. Comments submitted in the consultation period are preferred as this enables the planning department to identify the key issues to be addressed with the applicant at an early stage in the process. Notwithstanding this, any comments received beyond the consultation expiry date and prior to decision will be taken into consideration.
“The determination date for the application has not yet been decided but is expected later this year.
“To date, a significant number of comments have been received. These all need to be checked before being loaded onto the portal and understandably this takes time. They will however all be taken into consideration before a decision is made.”