What are the best bus/train tours for New England during the fall?

Answer 1

There are a few different options. The first is majority bus with a one day scenic train tour. It's called New England, Cape Cod & Martha's Vineyard Autumn Foliage.
http://www.vacationsbyrail.com/usa/rail_tours/new_england_railway/index.html

The other has five scenic day train tours and three river boat cruises. It's work checking out. New England Rails and Sails
http://www.vacationsbyrail.com/usa/rail_tours/new_england_trains/index.html

Answer 2

Go visit The New forest in Hamshire
It is spectacular in Autumn
by coach , car or trailer

follow the West coast by train to Scotland
Breathtakingly beautiful

have fun
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Sorry
i misread your question;
New England sounds wonderful but i have never been to the USA
I am sure the tourist board will have some spectacular routes available for you
Have a lovely holiday when the time comes

:)