Mrs Wright said the bad driving was not particularly unusual, given what had been seen daily on the roads recently, but on Monday she remembered to get evidence so videoed it.
"You see it all the time, but not this bad."
As they approached Franz, Mrs Wright decided to confront the driver when the car, containing three generations of a family-of-five, pulled over outside a holiday park about 2.30pm.
"I tapped on the window. I said, 'I need to have your keys'. He looked at me vacantly."
After a fair amount of "screaming" to try to get the driver to understand, and the man's wife reasoning that it was "their first time" in New Zealand, she succeeded in taking the keys.
"We rang the Hokitika police to say we'd removed these keys."
They had since been contacted by police over the incident. "We haven't had a rap over the knuckles, as such," Mrs Wright said.
She said they had only done the responsible thing. At the very least, the lives of five people in the rental car had "been saved".
"It was just the fact that we'd followed them for so long and there'd been so many near-misses."
Meanwhile, West Coast police received a dozen reports of bad driving on the roads via its communications system yesterday. On top of that there were four crashes, Hokitika police said this morning.
In deep South Westland, Haast senior constable Robin Manera said his main focus in recent weeks had been fielding calls about traffic incidents.
"The radio doesn't stop all day [with complaints] -- the police radio is jammed," Mr Manera said.
The incident on Monday was a scenario that posed "a dilemma" for many motorists. While police did not necessarily condone such direct action, it followed the sentiment of a television campaign which encouraged people to stop drink-drivers.
He said burgeoning tourist numbers this summer had affected driving conditions recently, fortunately so far without tragic consequence in South Westland.
"There's an awful lot of traffic about but we haven't had the trauma that normally comes with it -- but we're not going to kid ourselves," Mr Manera said.