The sometime race car driver was behind the wheel of a 1962 Corvette - with wife Karen at his side - when the engine stalled as he made the ceremonial first drive up to State Highway 6.
With about 50 people watching, Mr Boult quickly restarted the engine and pulled away with a resounding screech of tyres.
The $6.4million project, which started last September, joins an existing underpass at the Shotover Bridge with a single-lane connection to the Frankton-bound lane of the highway.
As traffic volume on the highway continues to grow, the slip road provides safer access for right-turning Quail Rise and Tucker Beach residents than the Tucker Beach Rd intersection.
NZ Transport Agency South Island director of regional relationships Jim Harland said Quail Rise's Greg Thompson and other residents "very forcefully'' brought the intersection's safety risks to its attention.
However, the resort's traffic congestion problems remained, and the agency would work on solutions with the district and regional councils over the next 12 to 18 months.
Those included greater use of public transport, encouraging walking and cycling, and "getting more vehicles down [Highway] 6A into town''.
"We've just got to find some funding to make these things happen.''
Mr Thompson said he had a "light bulb moment'' in 2014 while sitting in a queue of vehicles waiting to turn right on to the highway.
Because the underpass was already there, a slip lane was a straightforward and relatively cheap solution.
He started a lobbying campaign with a letter to the agency and an article in the Mountain Scene.
Mr Boult said it "took a little while'' for the agency to approve the slip road, but thanked it for listening to the community and council's concerns.
The project includes the installation of new water and wastewater pipes under the highway to enable more residential subdivision at Quail Rise.
NZTA project manager Phil Dowsett said the pipes had been laid and tested, and the last section of the highway would be sealed in about a fortnight.
