ROY, Utah — A small plane crashed on the side of Interstate 15 Sunday afternoon, sending both occupants on board to the hospital.

Around 3:30 p.m., a single-engine Piper Cherokee crashed between I-15 and I-84, according to Federal Aviation Administration officials.

There were two male occupants on board the plane and were both seriously injured. One was flown to the hospital and one was transported by ground ambulance. Police believe their injuries are not life-threatening and that they may have been a flight instructor and student.

The FAA said the plane crashed shortly after departure. It struck a billboard before coming to rest on the southbound side of the freeway.

Police say several witnesses stopped to help the occupants get out of the plane. One sustained a minor injury in the process.

The FAA and National Transportation Safety Board will conduct an investigation that will likely take about a year to complete.

Southbound I-15 lanes are closed; traffic is being diverted onto I-84.