Interstate 91 (abbreviated I-91) is an Interstate highway in the New England section of the United States. It provides the primary north-south thoroughfare in the western part of New England. The interstate's southern end is in New Haven, Connecticut (map) at Interstate 95; its northern end is at Derby Line, Vermont, a village in the town of Derby, at the Canadian border, where it continues as Autoroute 55. The largest cities along its route are New Haven and Hartford, Connecticut, and Springfield, Massachusetts.

Interstate 91 is 290 miles (467 km) long and runs nearly straight north and south through the U.S. states of Connecticut (for 58 miles, 93 km), Massachusetts (for 55 miles, 89 km) and Vermont (for 177 miles, 285 km). (The net distance as the crow flies is 259 miles (417 km), and the net direction is 9.0 degrees clockwise from north or south, i.e. northeast by north or southwest by south.) Interstate 91 parallels U.S. Route 5 for its entire length in all three states, and many of the Interstate's exits provide direct or indirect access to the older U.S. Highway.

I-91 map