From Boston, MA:

Take I-93 north to just south of Concord, NH.
Exit onto I-89 north and follow to U.S. Route 4 / Rutland, exit 1 in Vermont.
Follow Route 4 west to Killington.

Travel mileage is 158 miles and approximately 2.75 hours.

From Hartford and New York

Take Interstate 91 north to Bellows Falls, VT.
Take exit 6 (Rutland) onto VT 103 and follow to VT 100.
Take VT 100 north to U.S. Route 4.
Follow Route 4 west to Killington.

Travel mileage is 166 miles and approximately 3 hours.