The new Maungatapu underpass will be handed over to Tauranga City Council in the next month or so.

After nearly three years of construction, the underpass opened to public traffic overnight on Thursday.

Local road police said it was incident-free.

Underpass project manager John McCarthy lighter Friday traffic probably helped with the quiet opening morning.

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He expected it would take a week to 10 days for traffic to adjust to the new roading layout and urged people to take care.

McCarthy said the New Zealand Transport Agency-funded project would be delivered within the $45 million budget and three-year timeline.

"It's been no mean feat considering the weather we've had.

"These projects take a lot of work and a lot of time even before they get to construction. There is a real feeling of accomplishment when they can see the finished product."

Thanks to our 10-year-old passenger for filming this.

He said the 120 metre-long, two-lane link between Welcome Bay Rd and Turret Rd was unusual in the sense that it was a central Government-funded project where most of the work happened a local road.

The main purpose of the underpass was to reduce congestion on State Highway 29A and the roundabout above by separating out local Welcome Bay traffic.

"It's a bit like working on your neighbour's house to make yours better," McCarthy said.

As a connection between two local roads, the underpass would soon be handed over to the council.

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He said there was about a month of work left to complete the project, mostly centred on Hairini St.

A footpath and cycle lane needed to be connected across Hairini St to the existing lane on Turret Rd.

The end of the street, where it merges with Turret Rd, will be converted to a bus-only merging lane, while a separate give-way controlled diversion will be built off the street for other traffic.

The exising Hairini St merging lane will be turned into a bus only lane, while cars will be diverted to a give way-controlled intersection with Turret Rd. Graphic/Tauranga City Council
The exising Hairini St merging lane will be turned into a bus only lane, while cars will be diverted to a give way-controlled intersection with Turret Rd. Graphic/Tauranga City Council

McCarthy said this would both reduce the pressure on the stretch where three lanes merged and discourage people from using Hairini St as a rush hour rat run instead of going through the roundabout.

"It won't be an attractive option."

Hairini St may be delayed or closed in off-peak hours while the work takes place.

If a give way was not enough to discourage rat runners, something like Auckland's onramp metering lights could be used.

Tauranga City Council said when it announced the bus lane plan that the lane would also allow the bus to pass about 110 stationary cars.

Maungatapu underpass by the numbers

- $45 million
- 120 metres long
- 550 people worked directly on site during construction, estimated
- 400 worked off-site, e.g. precasting bridge beams
- 210 intersecting concrete piles used to construct underpass walls
- 2125 truckloads of dirt excavated during initial earthworks
- 36-metre long new steel overbridge installed for walking and cycling
- 34-tonne overbridge built and lowered in one piece, and can be removed for maintenance.

Source: New Zealand Transport Agency