Motorists are being warned to expect a "huge amount" of road works this summer.
The Transport Agency's general manager of transport services Brett Gliddon told a parliamentary select committee today the Agency planned to do double its usual road maintenance and renewal this year.
He says that would include ripping up and replacing sections of road and putting down harder road surfaces to cope with bigger trucks.
"We've got our biggest maintenance renewal program for the last 10 years happening this summer," says Brett.
"So it's about a 9 per cent investment across the network. We've been running at about 4 or 5 [per cent]. There's going to be a huge amount of roadworks on the roads this summer.
"As we've seen on a number of our networks, the increase in heavy vehicles has been significant, especially in places like the central Waikato.
"We're actually even changing the design, going for much longer-life pavements, rather than short-life pavements that we have to keep renewing."
The bills for this type of work are large, from Awapuni Road on State Highway 35 upgraded in April for $2.5m, to almost $100m being spent on investigating and fixing damaged road surfaces on sections of the Waikato and Kapiti expressways that are just a few years old.
Since 2010, law changes have allowed increasingly long and heavy trucks - now more than 50 tonnes - on highways, well beyond the earlier 44-tonne limit. The vehicles' power has in some cases doubled to 700 horsepower.
In 2012, slightly more than 10 per cent of freight was carried by these larger trucks. This tripled by 2017 to more than one third.
An updated figure for 2019 is being sought.
The proportion of highway opened up to these bigger trucks has also kept rising, from 45 per cent of all highways in 2016, to 8225km - 71 per cent this year - by adding 1004km on key regional routes.
Allowing more large trucks - called high productivity motor vehicles - on more roads is one of five key priorities of investment over the next two years outlined in NZTA's 2018-19 annual report.
State highways cost more than $20,000 per kilometre to maintain each year.