Simplify the following text for a Grade 8 native English-speaking person.
Original: This list , by their present names , of heavy rail passenger stations in the Greater London region excludes stations served only by the London Underground , Tramlink and Docklands Light Railway systems .
Simplified: The list includes National Rail and Heathrow Airport stations . It does not include stations exclusively served by the London Underground , Tramlink and Docklands Light Railway .