The One Mile House Interchange in Saint John is proving to be the most expensive highway exit ever built in New Brunswick as its contruction runs 70 per cent over budget.

Designed in part to aid construction of a promised second Irving Oil Ltd. refinery, the off ramp was to cost $43.5 million when announced in 2007.

But the latest estimate is that it will now cost $75 million — 70 per cent more than the original estimate.

Irving Oil cancelled its plans to build the refinery, but the interchange went ahead anyway despite ballooning costs.

Crews have been working on the interchange on the Saint John Throughway for two years, and it will take another year for it to be finished.

Saint John Mayor Ivan Court said the interchange is still a good project for the city, even though it was meant to divert increased truck traffic expected from a second oil refinery.

"The sooner that One Mile gets built and finished, the better," Court said Monday.

Court said that two-thirds of the way into the job, there's no stopping now.

"You're in now. If you're in for $48 million or you're into it for $70 million, you've got to complete the project," Court said.

The mayor said he knows some residents don't understand why so much money is being spent on an off ramp when many city streets remain in a state of disrepair. But, he said the interchange isn't costing the city a dime.

The project is being paid for by the federal and provincial governments, Court said, and it will be a welcome addition whatever the price tag.