Simplify the following text for a Grade 11 native English-speaking person.
Original: It was due to be delivered to London Underground by the end of 2006 for testing on the Victoria line during engineering hours ( times after the line stops carrying passengers and repair and testing work is carried out ) , but this did not occur until May 2007 .
Simplified: It was due to be delivered to London Underground by the end of 2006 for testing on the Victoria line during engineering hours but this did not occur until May 2007 .