I used to live in west London over 30 years ago, and I remember the M40 ran from Uxbridge (where it started) to Oxford, where it stopped. I sometimes used it to go to Oxford for the day at weekends.
It originally stopped at Oxford, and it was years before it was joined up to Birmingham (1989/90).
I often wondered why they built it to Oxford and then no more, as it was hardly a major route for traffic and heavy goods vehicles.
I remember in "Yes Minister" it was said that motorways were built from London to Oxford and Cambridge (before being built to say Southampton) because all the transport Civil Servants attended either Oxford or Cambridge universities.