CHICAGO — A Chicago Transit Authority train collided with a standing train at a station in a western suburb of Chicago, during the morning rush hour on Monday, Sept. 29, leaving at least 33 people injured.

The collision happened at about 7:45 a.m. local time at the ground-level Harlem Station in Forest Park, west of Chicago. Those who were injured were transported to nine area hospitals with what appeared to be non-serious injuries, including the operator of the standing train.

The National Transportation Safety Board said it was sending investigators to Chicago to investigate the collision. The CTA also is investigating to see whether there was an operator or anyone else on the colliding train, which had no customers.