The Lake Forest police and fire departments responded to a crash on northbound Route 41 at Westleigh Road at about 4:10 p.m.
Police said a motorcyclist, identified only as male, was driving a 2017 Suzuki northbound on Route 41 when it tried to pass between a 2019 Kenworth semi-tractor with a loaded trailer in the curbside lane and another vehicle in the inside lane. That maneuver is known as "lane-splitting."
While trying to pass in between both vehicles, the motorcycle struck the rear driver's side of the trailer, police said. The motorcyclist was ejected and killed immediately.
The victim's name was not immediately released, and the driver of the semi was not injured.
The crash is being investigated.