Simplify the following text for a Grade 10 native English-speaking person.
Original: Class 139 is the TOPS classification for PPM60 model lightweight railcar units built by Parry People Movers for use on the national rail network in Great Britain .
Simplified: British Rail Class 139 is the TOPS classification for PPM60 model lightweight railcars built by Parry People Movers , for use on the British rail network .