Waka Kotahi has discontinued its practice of filling potential long-tail bat roosts in the path of the Mt Messenger bypass route with builder's foam.
Last year RNZ revealed the transport agency was using the technique to encourage the endangered mammals to avoid the route on State Highway 3 in Taranaki.
The practice risked bats being trapped inside roosts.
Environmental manger for the project, Roger McGibbon, said contractors now attached neoprene flaps over potential roosts instead.
"That method has been amended somewhat, so that rather that filling the holes with builders foam or some other product were going to put flaps on them now.
"So that by any remote chance there's a bat still in one of those holes and it wasn't detected these flaps allow a bat that's inside the tree to leave but not any new ones to come back in."
McGibbon said the Department of Conservation approved the use of building foam.
"That was an accepted practice at the time we did it and it was done under their jurisdiction and support.
"It was just to stop bats reoccupying trees that were targeted to be felled."
Hundreds of trees suitable for bat roosts will be felled as part of the $280 million project.
McGibbon said each of these trees would be cleared of bats before they came down.
"And the felling of those trees must occur in daylight immediately after that clearance has occurred."
McGibbon briefed media this week on the ecological restoration programme that accompanied the project which involved felling 32 hectares of native bush.
He was comfortable with that in the circumstances.
"In isolation all on its own it would always be an issue taking down native forest that we don't have a lot of, but the product or end result after the mitigation and pest control once it kicks in and has effect will generate benefits that will leave that forest in the Parininihi White Cliffs area in far better condition than it is currently."
Waka Kotahi has committed to a pest management programme in perpetuity over 3650 hectares on either side of the bypass, including 250 kilometres of trap lines with devices and bait stations every 100m to 150m.
McGibbon said the pest programme would initially employ 20 to 30 people fulltime before settling down to between 12 and 20 staff.
It was hoped it would enable threatened species such as kiwi, long-tailed bats and kōkako to thrive in the area once more.
It was estimated for example, that the forest could sustain a population of 1200 kiwi, currently just six have been identified with territories that overlap the project footprint.
Although the Resource Management Act directed developers to "avoid" felling native forests, McGibbon said it allowed for such mitigation programmes.
"The RMA says avoid, remedy or mitigate ... so yes, we absolutely try to avoid [felling trees] at all costs, but to bring a road into North Taranaki that is safe to use you can't avoid impacting some native vegetation and I'm quite comfortable here that we've gone as far as we can to avoid as much as possible."
He said there was also a huge planting programme to offset vegetation loss.
About 120,000 natives will be planted in wetlands and along waterways and a further 100,000 along roadside margins and embankments.
The projects two single-span bridges - a 125m structure over the Mimi wetland in the south and a 30m bridge in the Mangapekepeke Valley - had been designed to have a minimal impact of the environment.
Similarly, a 235m tunnel at the summit of Mt Messenger was designed to create an ecological corridor from east to west over the bypass.
As an ecological restoration expert he had taken great pleasure working with mana whenua for the project Ngāti Tama, McGibbon said.
"Once we got this package resolved, the restoration package -- because Māori see things in the very long term, multi-generational - they could see that this to them was a road which was important economically but more importantly it was long-term multi-generational protection of their rohe.
"Some of the team perhaps rather flippantly use the description now that this is a restoration project with a road attached and I've done perhaps 20-25 roading projects in the past 20 years and by far that is the case here.
"And if you build on the cultural aspect the collaborative way we've gone about working on the mitigation and how that will kick into a programme that will endure for a long time, it's got a huge number of positives to it."
Enabling works for Te Ara o Te Ata Mt Messenger Bypass have begun and it's scheduled to be completed in mid 2026.
Further benefits of the project:
74 new jobs
$4 million in additional salaries in Taranaki
$25 million each year to be spent on goods and services supplied in Taranaki
