Inspector Dave Campbell said there had been no problems, but there were "quite a few more cars" than expected, with about 40 vehicles joining the event. Earlier estimates had put the number at 30.
If there was any trouble, it was likely to be today, he said.
All vehicles entering and leaving the city were stopped at a checkpoint on State Highway 1 at Pine Hill and police were informing the Canterbury students where the city liquor ban areas were.
Students in one van were told by police to spray-paint over offensive material on their vehicle.
Police at the checkpoint arrested a 24-year-old man, who was not a student, and charged him with drink-driving.
Police checkpoints were also set up in Oamaru, where a 59-year-old woman was arrested and charged with drink-driving, and 5km north of Rakaia.
Canterbury student Sunil Hira said the checkpoints seemed a bit over the top, but police were just doing their job.
"If that's what they have to do, that's what they have to do, but we are following the law."
Other students said they had been pulled over about seven times, but "each time police have been very good".
About 12 themed vehicles sporting slogans such as "Not by the hair of my chinny, chin, chin" and "Family violence, it's OK if you pay", left Christchurch about 11am and started arriving in Dunedin about 8pm.
Many carloads of students in unmarked vehicles were also on the road.
The official Undie event was cancelled this year following disorder in 2006 and riots last year in Dunedin, which resulted in 69 arrests.
Late last night, Insp Campbell said the Undie visitors seemed to be congregating around flats in the Castle St area.
There had been a couple of fires, including a mattress fire in the street which was put out by the Willowbank Fire Brigade about 9.45pm.
The other fire was a bonfire on private property.
Two people were arrested.
One charge was related to the lighting of a fire and the other to the use of cannabis.
