St. Patrick’s Day has long been one of the most dangerous holidays on the roads, and data released this week show that drunken driving violations skyrocket when the holiday falls on a weekend, as it does this year.

While the holiday officially is on Sunday, many people will celebrate Saturday. Denver-based Alcohol Monitoring Systems (AMS) said confirmed drinking violations will rise 23 percent on Saturday, compared to the average for St. Patrick’s Days that fall on other days of the week.

For offenders ordered by the courts to abstain from alcohol, violations will rise 50 percent. The firm based its findings on a study of data on 279,000 drunken drivers over the past 10 years.

In Minnesota, where the State Patrol will have extra troopers out looking for drunken drivers, there have been 11 St. Patrick’s Day deaths in the past five years. In that time, 1,241 motorists have been arrested for drunken driving, according to the Minnesota Department of Public Safety’s Office of Traffic Safety.

Since 2008, the number of Minnesota motorists stopped with blood-alcohol levels above the legal limit of 0.08 percent has risen steadily as the holiday moved closer to the weekend. In 2008, when St. Patrick’s Day fell on a Monday, the number was 165. In 2009 (Tuesday), arrests rose to 218, followed by 225 in 2010 (Wednesday), 287 in 2011 (Thursday) and 346 in 2012 (Saturday).

The State Patrol is preparing for a busy weekend as revelers head out. “Weekend-long events could make for a potentially dangerous situation on our roads,” said Donna Berger, director of the Office of Traffic Safety. “If you’re planning on drinking, plan ahead for a sober ride.”

Metro Transit and the Minnesota Valley Transit Authority will offer free rides on buses and light-rail trains on Saturday from 6 p.m. through the last scheduled trip. Many sober driver services and cab companies also will give partyers rides home for a fee.

AMS’ analysis looked at the behavior patterns of “hard-core drunken drivers.” Of its sample, 98 percent are diagnosed as alcohol-dependent. Hard-core drunken drivers are defined as those who have driven with a blood-alcohol concentration of 0.15 percent or above, or who are repeated drunken drivers, as demonstrated by having more than one impaired driving arrest.

“These are criminal offenders who know they are being monitored 48 times a day, and who know they will be caught. Now imagine the people out drinking — drinking and driving — who aren’t being monitored.”

In 2010, 80 percent of fatal accidents on St. Patrick’s Day involved a driver with a blood-alcohol level of more than twice the legal limit, said Mike Liams, CEO of AMS.

“It’s a holiday of extremes,” he said. “Don’t wait until you’re drinking to realize you may need to make a decision. Just make it in advance, and then safely enjoy your evening.”