Aucklanders driving to beach homes east of Warkworth stand to cut almost 16 minutes off holiday weekend trips via a $760 million motorway extension.
The Transport Agency, in a planning application unveiled yesterday, warns that worsening holiday traffic congestion without the new road would push average trips from south of Puhoi to the beaches turnoff east of Warkworth to 30.6 minutes by 2026.
That compares with 18.8 minutes at the start of holiday weekends now, and 13.9 minutes during weekday evening peak hours.
But with the 18.5km motorway extension, which is likely to be tolled and could be completed by about 2022 if a board of inquiry grants fast-track planning approval under national consenting rules, the agency predicts an average holiday weekend trip of only 14.8 minutes - four minutes shorter than now.
Trips to the top end of the new road, just north of Warkworth, would take just 10.7 minutes at the start of holiday weekends for those headed to Northland rather than doubling back to the beaches turnoff just east of the town's difficult Hill St intersection.
A report lodged with the Transport Agency application predicts average daily traffic volumes on State Highway 1 between Puhoi and Warkworth will increase from 17,400 vehicles to 25,000 by 2026 without the dual-carriageway motorway extension with two lanes each way.
Although it acknowledges the new road will induce greater overall traffic volumes, it expects just 14,000 vehicles a day to use the motorway, compared with 14,500 likely to stay on the old route.
But the agency argues the road will be more than what critics deride as a "holiday highway", saying it is needed to cope with a 51 per cent increase in freight movements to or from Northland by 2031, and that it will reduce crashes along what it says is now "primarily a single carriageway, two-lane rural highway with some passing lanes".
It warns that accidents are likely to increase.
The motorway extension - which will form the first stage of a "road of national significance" the Government ultimately wants built to Wellsford once engineers can design their way through tough geological challenges - will include 12 viaducts and bridges through what the agency describes as steep and rugged topography.
The highest viaduct will be 46m above ground level in the Perry Rd sector south of Warkworth, and the longest will be a 520m flyover of the existing SH1 south of Puhoi.
Substantial viaducts will also bypass the existing difficult highway climb over Schedewys Hill.
Northbound traffic will be able to leave the new motorway at Puhoi.