Authorities said a big rig carrying a load of sand smashed through the concrete median and landed on the Gold Line tracks at San Gabriel Boulevard just after 8 a.m.
According to the California Highway Patrol, the driver of a green Toyota Camry made an illegal lane change, forcing the big rig to lose control and crash into a pickup truck. Both the big rig and the pickup truck careened through the cement barrier and ended on the tracks.
No trains were involved in the accident.
Gold Line service was restored, but had to share the one undamaged track on the line. The undamaged westbound lane will carry trains in both directions between the Allen and Sierra Madre Villa stations.
A Metro spokesman said the eastbound tracks were bent and the concrete footings were skewed and cracked. It was unclear when that track would re-open.
Three people were injured in the accident. Two people were hurt in the pickup truck, and the other was in the big rig. CHP said they were taken to a local hospital for minor injuries.