Working under spotlights, engineers used lifting gear to start removing the engine and eight carriages from the track following Saturday's collision.
Nine-year-old Louella Main and Emily Webster, 14, were among those who died.
Police are investigating whether the car driver parked at the crossing because he wanted to kill himself.
They are also looking at whether the car had a fault which meant it could not be moved. A mobile phone found in the car is also being examined.
The driver has been named as 48-year-old Brian Drysdale from Reading.
Hospital
Louella was the youngest victim. Her mother, Anjanette Rossi, 38, also died.
A further 71 people were injured and many of them remain in hospital.
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