The bridge is expected to reduce traffic congestion, nighttime train horns and the possibility of deadly collisions.
The bridge spans from Sunset Avenue to Orange Avenue along Valley Boulevard.
Up to half of the nation's goods pass through these rail lines.
"The rest of the nation needs to understand that they need to help us pay for these separations in order for them to get on-time delivery which they treasure," said Rep. Grace Napolitano of the House Transportation Committee.
The project cost $96 million. It was paid for with state and federal funds.