This defines the extent of the operational network.
Route miles is the total extent of routes available for trains to operate.
Track miles takes into account multiple track routes (eg for each route mile where there is double track, there are two track miles; where there are four tracks, there are four track miles).
Detailed information about this measure is contained in Table A of the Sectional Appendix, published to railway industry parties. The details are published in the National Electronic Sectional Appendix (NESA).