NZTA regional manager of infrastructure delivery Jo Wilton said the project would not be finished by the end of September but there would be two temporary approaches in action.
A SH1 southbound lane closure was required beforehand, so a temporary tie-in to the intersection could be constructed.
That one-day closure will take place on September 24 from 7am, impacting Hamilton-to-Tīrau traffic.
Motorists will be required to detour via SH29, SH27, to SH1 adding about 12 minutes to travel times.
Northbound traffic would not be impacted, and access would remain for residents, school buses and emergency services. Traffic on SH29 and traffic on SH1 between Piarere and Cambridge would also not be affected.
Once the temporary tie-in was complete, the SH1 southbound lane was expected to re-open in the early evening of September 24.
The new layout would then mean SH1 southbound traffic would use the roundabout to turn onto the temporary road to carry on their journey.
SH1 Tīrau traffic heading to SH29 would also use the temporary tie-in road, with a give-way rule in place, when turning right onto SH1 to the new roundabout and exiting at SH29.
SH1 Tīrau traffic heading north will enter a slip lane before merging with other northbound traffic.
The temporary arrangement was expected to remain in place until later this year.
Night works to undertake line marking ahead of the closure will be carried out on September 23 with stop/go in place from 7pm until 7am.
A one-day SH1 southbound lane closure is required on September 24 from 7am. Motorists will be required to detour via SH29, SH27, to SH1 adding around 12 minutes to journey times. Graphic / New Zealand Transport Agency
A temporary speed limit of 60km/h remains in place around the project site to protect road workers.
NZTA asked people to take extra care when travelling through the area and work zone.
Construction of the $43.5 million roundabout began in January and is on track to be finished in mid-late 2025.
It will have three approaches, along with a fourth stub for the future expressway.
Traffic travelling north from Tīrau on SH1 will use a temporary road to connect to SH29. Graphic / New Zealand Transport Agency
Southbound closure and detour information
The 1-day SH1 southbound closure will take place on September 24 from 7am (work is weather-dependant).
Traffic travelling south on SH1 from Hamilton to Tīrau will be required to detour via SH29, SH27, to SH1.
Traffic travelling to Matamata/Tauranga on SH29 will continue as normal.
Traffic travelling north from Tīrau on SH1 will use a temporary road to connect to SH29 by the roundabout, where they can continue to SH1 (using the roundabout) or SH29.
Traffic travelling to Cambridge or Hamilton from SH29 to SH1 will travel through the roundabout.
Traffic travelling on SH29 to SH1 (Tīrau) will turn left onto the temporary road and connect back to SH1.
