Complex sentence: The New York, New Haven and Hartford Railroad (commonly New Haven), was a railroad that operated in the northeast United States from 1872 to 1968 which served the states of Connecticut, New York, Rhode Island, and Massachusetts.
Split into simpler sentences: The New York, New Haven and Hartford Railroad was a railroad that operated in the northeast United States from 1872 to 1968. Commonly referred to as the New Haven, the railroad served the states of Connecticut, New York, Rhode Island, and Massachusetts.