MINNEAPOLIS (AP) — Several large marijuana busts along Interstate 94 have authorities in North Dakota, Minnesota and Wisconsin wondering whether the interstate corridor is becoming a major smuggling pipeline for marijuana and other drugs.

Authorities think more residents in the three states are buying marijuana where it's legal and then bringing it back home to distribute, The Star Tribune reported . While Minnesota legalized medical marijuana in 2014, recreational use remains illegal in Minnesota, Wisconsin and North Dakota.

Minnesota troopers seized more than 2,600 pounds of marijuana last year, more than six times what was confiscated the year before. North Dakota troopers confiscated 300 pounds last year, an 88 percent increase from 2016. Wisconsin troopers saw a 20 percent increase in drug arrests from 2016 to 2017.

"That's not the direction we want to go," said Wisconsin State Patrol Lt. Chris Jushka. "We're definitely seeing more drugs in the state."

One of the first large busts occurred in November. Police pulled over a Minnesota woman for speeding in North Dakota. A police K-9 discovered almost 290 pounds of marijuana estimated to be worth more than $1.3 million.

One of the biggest discoveries was in January, when authorities in North Dakota found more than 470 pounds of marijuana worth more than $3 million during a routine traffic stop for a minor driving infraction.

Wisconsin State Patrol plans to add another K-9 to its force of eight dogs and will increase trooper training. Minnesota is adding two dogs to its K-9 unit, bringing the total up to 16.

"It's aggressive enforcement, but it has to be partnered with a strong prevention message," said Brian Marquart, the Minnesota Department of Public Safety's gang and drug coordinator. "People say that marijuana is a safe substance. . It is very addictive. We just want people to stop dealing and stop using."