Motorists will not be able to use Trinity Road for a further 10 days after holes were found under the road.
The road, which has been shut throughout the school summer holidays for sewage network upgrades, was supposed to reopen today (1 September).
Voids were discovered beneath the carriageway last week which need urgent repair.
Environment & Infrastructure says they have considered other options, but the work that needs to be done is in the middle of the road.
"We understand the inconvenience this may cause and sincerely apologise for the disruption. However, addressing these issues now is essential to prevent future roadworks and further closures.
"We are engaging with affected businesses in the area to provide support and minimise the impact of the extended works.
"Public safety remains our top priority, and we appreciate your patience and understanding as we complete these critical infrastructure upgrades."
A new completion date of 10 September has been set.
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