After 30 years, Baldwin St lost the Guinness World Records title earlier this month to Ffordd Pen Llech, in the North Wales town of Harlech.
Clark Fortune McDonald and Associates Dunedin branch manager and licensed surveyor Toby Stoff said he wrote to Guinness World Records, raising a technical issue with the way the winding Welsh lane was measured before it was awarded the steepest street title.
He said it was measured on "the inside sealage of a horizontal curve'', which went against good surveying practice, because road gradients should be measured at the centre line.
Now he is setting out to convince Guinness that the Welsh street was measured incorrectly, and to adopt the centre line methodology.
"You can't just measure from the left to the right, just because it happens to be convenient for your purposes. This thing needs to be measured objectively.
"I haven't heard back from Guinness yet, so what I'm doing in the meantime is I'm getting statements of support for the centre line methodology, from experts in the surveying and engineering industry.''
He is already getting good responses from New Zealand experts, and is working on getting support from European and North American experts, so his case does not appear to be biased.
Mr Stoff said staff from Global Survey New Zealand planned to scan Baldwin St using the centre line methodology, to provide accurate benchmarks for geo-referencing.
It was hoped the same could be done on Ffordd Pen Llech, so an accurate comparison could be made.
"We need to do it, so that we're comparing oranges with oranges, not apples and oranges like we're getting at the moment.
"The issue is convincing Guinness that there's an error and that the methodology needs to be changed.
"She'll be a long, hard road. It could take years, but the journey has started.''
