The new interchange at the State Highway 2 and 29A intersection in the Bay of Plenty is set to fully open to traffic in mid-August.
The Te Maunga interchange at Baypark has been operating without its fourth ramp since its partial opening last year.
Waka Kotahi said the remaining ramp will temporarily take all traffic from SH2, the Tauranga Eastern Link (TEL) and Pāpāmoa.
It said this change would allow work on SH2 at ground level, underneath the interchange, to be completed.
The work to make the switch, which includes opening the ramp, commissioning the new traffic lights at the interchange and the closure of SH2 northbound underneath the interchange, is set for 13 August to 16 August.
The transport agency's regional manager of infrastructure delivery Jo Wilton said she was looking forward to completing another piece of the project's puzzle.
"We're in the last stages of the Bay Link project and this piece takes us a huge step closer to overall project completion.
"Opening the remaining ramp to traffic means changes for people travelling on SH2 from Pāpāmoa and SH29A from Maungatapu, and will require all drivers to use the newly signalised interchange with the current lane under the interchange temporarily closing.
"This will streamline traffic, removing the merge from two northbound lanes to one on TEL and simplifying lane selection for those travelling to the Bayfair roundabout or Bayfair flyover."
Wilton said the new ramp would be open to the public under temporary traffic management from early morning on 15 August and remain open during daytime hours, from 6am to 7pm.
Once the traffic switch was completed, the ramp would be open 24/7.
"For people travelling from SH2 or Pāpāmoa we're expecting traffic to be slower, due to the signalised interchange, but better managed which will improve flow at the Bayfair roundabout.
"Overall travel times may increase slightly following the initial period of adjustment for road users.
"While there's further work required that needs to take place from now until opening date, we want people travelling from SH2/Pāpāmoa and SH29A/Maungatapu to be aware of the upcoming switch."