Basis for tracking transport overnight? (7,7)

'basis for tracking' is the definition.
(part of a railway track)

'transport overnight?' is the wordplay.
I cannot really see how this works, but
'transport' could be 'sleeper' (sleeper is a kind of transport) and 'sleeper' is found in the answer.
The remaining letters 'railway' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...