Simplify the following text for a Grade 10 native English-speaking person.
Original: Route Availability ( RA ) is the system by which the permanent way and supporting works ( bridges , embankments , etc ) of the National Rail network of Great Britain are graded .
Simplified: Route Availability ( RA ) is the system by which the permanent way and supporting works ( bridges , embankments , etc. ) of the National Rail network of Great Britain are graded .