Simplify the following text for a Grade 5 native English-speaking person.
Original: In 1972 an extension of the M1 was opened into central Leeds as the Leeds South Eastern Motorway where it met the Leeds South Western Motorway ( M621 ) coming north-east from the M62 at junction 3 .
Simplified: In 1972 an extension of the M1 was opened into central Leeds . It was called the Leeds South Eastern Motorway .