(KTRS) – One engineer was taken to the hospital for a checkup after two of the St. Louis Zoo’s trains collided Friday afternoon.

Zoo officials say more than 150 visitors were on the trains at the time of the accident, but none were injured. One train was going 8 miles an hour when it ran into the back of a second train. The zoo says mechanical problems are not to blame for the accident.

The trains should be running again by Saturday morning.