SACRAMENTO (KRON) — Caution tape blocked off tracks and two regional transit trains in Sacramento all day Friday.

 Six investigators with the National Transportation Safety Board arrived hours after a collision that injured more than 20 people and sent 13 of them to the hospital. 

The majority of them suffered minor injuries.

Sacramento’s Regional Transit officials say Thursday night, a train carrying passengers rear-ended an empty train undergoing maintenance testing.

 In a statement, a spokesperson wrote, “SacRT is saddened for all that were impacted by the accident, but grateful that there were no serious injuries.”

The cause of the collision now at the center of three separate investigations.

The NTSB, the California Public Utilities Commission and Regional Transit system are conducting their own.

SacRT officials say this is the system’s second crash in its 32 year history, and that its safety record remains one of the top in the transportation industry.