The study, called 'Have New Zealand’s Highest Risk Highways Improved?', finds that fatal and serious crashes have reduced by more than twenty percent across thirty-five historically high‑risk state highway corridors, despite traffic volumes increasing by around fifty percent over the same period.
Prepared by WSP Technical Principal - Road Safety Mark Newsome, the research provides one of the most comprehensive longitudinal assessments of whether decades of targeted road safety investment have delivered meaningful harm reduction outcomes.
“This research confirms what Safe System principles tell us. That when we invest in the right infrastructure, we can dramatically reduce deaths and serious injuries, even as traffic continues to grow,” says Mark.
Infrastructure investment is delivering results
Mark's analysis revisited corridors first identified as high collective risk under the KiwiRAP programme in 2008 and compared crash outcomes across two five‑year periods: 2002–2006 and 2017–2023 (excluding COVID‑affected years).
Across all corridors studied, fatal and serious crashes reduced by 20.4 percent, compared with just a 4.6 percent reduction across the wider rural road network.
The strongest results came from highways that had received significant safety upgrades such as bypasses, partial bypasses, motorway extensions, and continuous median or roadside barriers. On these routes, fatal and serious crashes fell by 28.4 percent on average.
Some corridors achieved dramatic improvements. For example, SH20B to Auckland Airport recorded an 86 percent reduction in fatal and serious crashes. SH2 Bethlehem to Mount Maunganui saw a 78 percent reduction, and SH1 from SH74 to SH73 in Christchurch recorded a 64 percent reduction.
“These are not marginal gains,” says Mark. “They represent hundreds of lives saved or serious injuries avoided. The evidence is clear: major, well‑planned infrastructure intervention works.”
Not all corridors are improving
While the overall trend is positive, the findings also highlight corridors where serious and fatal crashes are not reducing or are still increasing.
Six highways recorded increased crash numbers over the study period, including: SH1 Cambridge to Piarere, with a 75 percent increase, SH2 Katikati to Tauranga, up 44 percent, SH1 Marsden Point to Whangārei, up 23 percent, and SH1 Auckland to Takanini, up 13 percent.
In most of these cases, the research found that either no significant safety upgrades had occurred, or improvements were too recent to yet be reflected in long‑term crash data.
“This is a critical insight for decision‑makers,” says Mark. “Where we haven’t invested meaningfully, the risk remains - or worsens as traffic volumes increase. KiwiRAP was designed to highlight exactly this, and the programme has proven its value.”
A clear case for Safe System investment
The research reinforces the importance of a Safe System approach, where infrastructure is designed to minimise the likelihood that mistakes lead to fatal or serious outcomes.
Bypasses remove conflict from town centres, median barriers prevent head‑on crashes, and motorway‑standard corridors reduce the complexity and severity of crashes when they do occur.
According to the study, corridors that received only minor treatments achieved an average crash reduction of just 4.3 percent, highlighting that incremental changes alone are not enough on high‑risk routes.
“Transformational improvements deliver transformational results,” says Mark. “This research shows that when funding is aligned with risk, the returns in human and economic terms are substantial.”
Informing future investment decisions
The findings come at a critical time, as New Zealand grapples with how best to prioritise transport investment amid growing demand and fiscal constraints.
The report identifies corridors where investment has clearly paid off, routes that remain high risk due to limited intervention, and locations where recent upgrades should be closely monitored to confirm long‑term benefits.
For Mark, the message is straightforward.
“If the goal is to reduce deaths and serious injuries, the blueprint already exists. We know which corridors need attention, and we know what works. The challenge now is maintaining the commitment to evidence‑led investment decisions.”
The full findings, including corridor‑by‑corridor analysis, can be found in the AA Research Foundation’s final report, ‘Have New Zealand’s Highest Risk Highways Improved?’.
