In addition to improving congestion at peak times, the underpass will make travel safer and easier for pedestrians and cyclists.
He said the successful contractor was expected to be announced in about two weeks. Once the design was confirmed, preliminary erosion and sediment earthworks would commence, leading to construction of the underpass beginning in July.
The start of the main construction will coincide with the completion of a new $750,000 Scouts and Girl Guides centre to replace the old hall displaced by the underpass.
Marra Construction will begin building the new Baden Powell Centre before Christmas on Ila Park in the neighbouring suburb of Ohauiti.
Mr Johansson said the underpass would take about three years to build at an estimated cost of $55 million. The project will deliver a two-lane link underneath the Maungatapu roundabout, connecting directly into Welcome Bay Rd.
"In addition to improving congestion at peak times, the underpass will make travel safer and easier for pedestrians and cyclists," he said.
The project was also in response to the growing pressure on State Highway 29, which was a "nationally significant" link between Waikato and the Port of Tauranga.
The $55 million underpass was in addition to the $750 million invested by the agency in the city's eastern corridor including the motorway that will bypass Te Puke, the planned Baypark to Bayfair upgrade, and the completed Hewletts Rd flyover and second Harbour Bridge.