RANCHO CUCAMONGA, Calif. (KABC) -- A motorcyclist was killed after a crash involving a big rig on the 15 Freeway in Rancho Cucamonga, prompting an hours-long closure of southbound lanes.The crash occurred on the southbound side of the freeway near 4th Street at approximately 11:34 p.m. Monday. Three lanes later reopened at around 4 a.m. Tuesday, according to the California Highway Patrol.Police say the motorcyclist went underneath the big rig, causing the big rig driver to swerve and crash. It was not known what led the motorcycle to hit the big rig.The driver of the big rig is expected to be OK.Video from the scene showed the cab of the big rig engulfed in flames. As many as three fire engines helped extinguish the blaze.The crash caused fuel to go into storm drains, officials said.The identity of the person killed was not known.