Dave Arquati wrote in
:

There is software available to companies involved in transport
planning which can plot "isochrones" (contours of time) of public
transport journey time to a specific point in London.

Unfortunately I can't immediately see any available on the internet.

Thanks - if you are able to find anything then please report back - it's
something I'd often wondered about and would have thought something would
have been available !

Many thanks
Richard