The A404 is a road in the United Kingdom that starts at Paddington in London and terminates near Maidenhead in Berkshire. The road initially follows a course through north-west London via Harlesden, Wembley, Harrow, Northwood and Rickmansworth. The M25 Junction 18 is at Chorleywood. The A404 crosses into Buckinghamshire and continues towards Little Chalfont and Amersham. Between Paddington and Amersham, the road closely follows the route of the London/Harrow-on-the-Hill/Aylesbury railway lines, The Chiltern Line, from Marylebone, and runs near several stations along that line.