blazer8696 has put together a 28.1 mile rail trail excursion from Farmington CT to Southwick MA on EveryTrail.com. This is a rail trail along the mainline built by the New Haven & Northampton. The portion shown is the northern section from Farmington, CT to Southwick, MA.
In CT it’s called the Farmington Valley Greenway. In MA it has multiple names including the Columbia Greenway and the Southwick Rail Trail.
Several miles south of Farmington the trail begins again and continues to the Cheshire town line. South of that the trail begins again in Cheshire and continues south to New Haven. Someday all these bits may be connected.
This is a paved trail and can be easily ridden on a street bike.
More details can be found at http://www.everytrail.com/view_trip.php?trip_id=794814