The flashing road cones loom, fluoro-clad police wave and another car is motioned to pull over.
Acting Sergeant Tim Coudret, of the Otago Coastal impairment prevention team, likens the breath-testing process to a train track — "Once you’re on, you can’t get off."
People react differently to being pulled over, whether they have been drinking or not.
Sgt Coudret once had an intoxicated man eat and spit out a paper copy of the breath-testing form.
"People do all sorts to get out of it," he said.
Sitting opposite me in the clinical-white interior of Dunedin’s mobile road safety base — better known as the booze bus — Sgt Coudret ran me through the process for an evidential breath test, as if I was a driver who had failed the initial roadside screening test.
"You are required to undergo an evidential breath test without delay," he said.
"If you fail or refuse to undergo the evidential breath test, you will be required to permit a blood specimen to be taken," said Sgt Coudret.
I was told I had the right to talk to a lawyer and given 10 minutes to decide if I wanted to have an evidential blood test, during which officers were not allowed to interact with me.
"It’s the most awkward 10 minutes," Sgt Coudret said.
Under the harsh florescent lights, he made me blow a lungful of air into his breathalyser.
As expected I passed. But among the drivers being processed outside, some had chosen to run the gauntlet.
The large checkpoint in Cumberland St, outside the Leviathan Hotel, last Saturday was part of Operation Summertime, which tested 4290 Dunedin drivers across six checkpoints over the weekend.
Officers — supported by a traffic management team from Waka Kotahi New Zealand Transport Agency and representatives from the city council and the Automobile Association — detected alcohol on the breath of 106 drivers.
Of those, 17 were processed for excess breath alcohol.
Ten will appear in court, with another four drivers waiting for the result of blood tests.
In the three days leading up to the operation, a further 2904 drivers were tested, 20 of whom had been drinking. Three of those were found to be over the legal limit of 250 micrograms of alcohol per litre of breath.
The numbers were "disconcerting", Sgt Coudret said.
People knew that if they were drinking they should not be driving, he said.
"It’s not rocket science," Sgt Coudret said.
It sometimes took enforcement action for the message to sink in, for which he made no apology.
Often after people were processed for drink driving, officers would give them a ride home, which made for particularly sobering conversations, Sgt Coudret said.
The talks were about treating people as humans, trying to understand their decisions and trying to prevent them from doing the same thing again.
"If you’re choosing to drink alcohol, do not drive — it’s a simple message," Sgt Coudret said.
Southern police would be stepping up enforcement this summer and drivers could expect to be tested anytime and anywhere — rural, urban or suburban.
While it was easy to have a barbecue and hit the road during spells of good weather, it was crucial that people had a plan to get home without putting themselves or others at risk.
"Every one of us on my team have been the first on the scene to fatal crashes ... We’ve all seen it far too much," Sgt Coudret said.
Over the 15 years he had been an officer, he had knocked on half-a-dozen doors to inform family members their loved ones would not be coming home.
"I’ve been the first on the scene to a number of fatals and I’ve dealt with a number of drivers who have crashed and killed their mates ... Every one of those was preventable, whether it was speed, alcohol or poor decision making," Sgt Coudret said.
"I've been in situations where people died after being trapped underneath cars, when they've died under there with me. I've been at scenes where people have had horrific injuries and you just have to do your best to keep them calm in those situations ... So if I can save one person from having a serious crash or injury or dying, then I’m happy," Sgt Coudret said.
There were some success stories, such as seeing cars full of lads with a sober driver.
However, over the years the amount of drink drivers caught had stayed stubbornly high and safer journeys could only become a reality if more drivers made better decisions.
"It’s everyone’s responsibility," Sgt Coudret said.