The accident closed all southbound lanes on LSD just south of North Avenue around 4 a.m. Those lanes reopened to traffic around 5:15 a.m.
Police said a motorcyclist lost control of his bike and fell off it. As emergency crews responded, two more approaching motorcyclists hit debris and slid.
Four people- two men and two women- were taken in critical but stable condition to Northwestern and Illinois Masonic hospitals.
The lanes were closed while crews cleared the debris.
