Simplify the following text for a Grade 12 native English-speaking person.
Original: The Tung Chung Line trains have been diverted to the new track since mid May 2003 , whereas the Mei Foo station interchange subway and the Nam Cheong station were opened at the same time the West Rail Line opened for public use in December 2003 .
Simplified: The Tung Chung Line trains have been running on the new track since mid May 2003 , whereas the Mei Foo station interchange subway and the Nam Cheong station were opened at the same time the West Rail opened for public use in December 2003 .