Certainly in Britain's case, many of the motorways built after WWII were based on pre-existing railway lines. Here are some examples:

A1(M)=East Coast Mainline - London Kings Cross to York and Newcastle.
M1=Midland Mainline - London St Pancras to Leeds via Nottingham and Sheffield / West Coast Mainline - includes Watford, Milton Keynes, Northampton and Rugby.
M2=Chatham Mainline - London Charing Cross and London Victoria to Chatham and Dover.
A3(M)=Portsmouth Direct Line - London Waterloo to Guildford and Portsmouth.
M3=South Western Mainline - London Waterloo to Basingstoke and Southampton.
M4=South Wales Mainline - London Paddington to Bristol and Swansea.
M5=Cross Country Route - Birmingham to Bristol and Exeter.
M6=West Coast Mainline - Coventry and Birmingham to Manchester, Carlisle and Scottish Border.
M8=Edinburgh to Glasgow Line.
M9=Edinburgh to Stirling Line.
M11=West Anglia Mainline - London Liverpool Street to Stansted and Cambridge.
M18=Sheffield to Doncaster Line.
M20=Kent Mainline.
M23=Brighton Mainline - London Victoria to Gatwick and Brighton.
M27=Southampton to Portsmouth Line.
M40=Chiltern Mainline - London Marylebone to Birmingham via Banbury.
M54=Wolverhampton to Shrewsbury Line.
M55=Preston to Blackpool Line.
M56=Chester to Manchester Line.
M62=Transpennine Route - Liverpool to Hull via Manchester and Leeds.
A74(M)=West Coast Mainline - Scottish Border to Glasgow.
M80=Glasgow to Stirling Line.
M90=Edinburgh to Perth Line.