Wrack St, which formed part of a key side-street link between Kamo Rd and Kensington Ave, was expected to have 300 to 500 cars diverted along it each day during the works.
"We already have some idiots on this road - and it's not only the young," said Wrack St resident Maureen Johnson. "So if we've got more being diverted, I'm not happy. More traffic will not be good."
Ms Johnson said she was concerned about the number of elderly people living on the street and hoped the council would be doing something to ensure their safety while neighbour Herbert Jenkins questioned why both projects were going ahead at once.
"It's going to be very awkward," Mr Jenkins said.
In response to resident concerns, WDC's Infrastructure Committee chairman Greg Martin spoke of "future proofing the city".
"These projects are on two of the district's busiest roads ... That means we are going to have an excellent result in about a year's time, but we are going to have to go through some pain before then," he said.
The decision to do both projects at once would mean cost saving and increased efficiencies, Cr Martin said. The end result would be a roundabout at the intersection of Kensington Ave and SH1, with a dedicated northbound lane so vehicles could travel through without stopping.
A central median barrier would be put in on the stretch between Manse St and Kensington Ave. This was part of a suite of six projects by NZTA along Whangarei's SH1, worth $37 million.
WDC would continue putting four lanes along Nixon St between Mill Rd and Kamo Rd.
What it means for drivers:
• Restricted traffic movements at both ends of Kensington Ave, including no right turns into it from SH1 or Kamo Rd
• No right turns into Nixon St from Kamo Rd, with diversions along Wrack St
• Manse St traffic will be controlled with temporary traffic signals
• SH1 remains open to through-traffic, with reduced speeds near Kensington
• Drivers are encouraged to plan alternative routes where possible
• Signs and publicity will keep motorists updated throughout the year