The guts of his idea is to knock down the traffic lights, build two roundabouts and dig out a couple of underpasses for pedestrians. Mr McLachlan said he's had the upgrade signed off by a number of industry mates in New Zealand and overseas who all told him it works.
And he also created a video which has already amassed more than 200 likes and 75 comments in 24 hours after he posted it on a Facebook page about traffic in Warkworth.
"You plan your life around that intersection. Even at non-peak times, it's a problem - it's a nightmare," Mr McLachlan said. "Auckland Transport are meant to pitch for Auckland, but they're not, so I thought I'd do their job for them."
And the New Zealand Transport Agency, the body in charge of the intersection, has not said Mr McLachlan's idea wouldn't work.
The agency's highway manager, Brett Gliddon, said it was aware of the challenges around the intersection and understood the frustrations of both the community and road users.
A variety of solutions had been investigated, he said, but the challenges lay in "how it would be implemented and constructed" because even a simple design would take time to complete due to consents, approvals then construction, which would cause a considerable amount of disruption.
"This means any short- to medium-term benefits would be discounted by the negative impacts during the construction period," said Mr Gliddon. "Ultimately the best solution to the current difficulties in Warkworth is to reduce the amount of traffic through the town centre by building the Puhoi to Warkworth motorway extension, allowing state highway traffic to bypass Warkworth."
Two years ago the Transport Agency decided to put off overhauling the intersection until after it builds a $760 million extension of the Northern Motorway which will take at least until 2021, subject to findings from a hearing next month of planning applications for the 18.5km extension to north of Warkworth.
