As attributive nouns, There's not usually much difference in meaning:

the rail / railway network

railway / rail transport

though rail is the more common variant nowadays.

As mass / nearly mass nouns, the definite article is never used with 'rail':

the coming of the railway/s

the coming of rail

though again, the terms are largely synonymous, with the shorter variant of even the rather dated expression given above gaining popularity in recent years.

Of course, the words as originally (and for some time later) used were not interchangeable: rails were joined with fishplates, and railways built to compete with canals. Even today, 'Rail was built ...' doesn't sound acceptable.

As attributive nouns, There's not usually much difference in meaning:

the rail / railway network

railway / rail transport

though rail is very likely the more common variant nowadays according to these Google Ngrams (which results agree with my own perceptions).

As mass / nearly mass nouns, the definite article is never used with 'rail':

the coming of the railway/s

the coming of rail

though again, the terms are 'largely synonymous', with the shorter variant of even the rather dated expression given above gaining popularity in recent years.

Of course, the words as originally (and for some time later) used were not interchangeable: rails were joined with fishplates, and railways built to compete with canals. Even today, 'Rail was built ...' doesn't sound acceptable.