Route 103 begins as a continuation of Quinnipiac Avenue at an intersection with Route 80 in the Quinnipiac Meadows at the Roundabout neighborhood of New Haven. It crosses into the Montowese section of North Haven after about , and meets with Route 17 (Middletown Avenue) after another . Route 103 continues north for another , then intersects with Montowese Avenue, which is an unsigned state highway (SSR 715) signed for I-91 (at exit 9), and also leads to the Universal Drive shopping area. Route 103 continues north, crossing the Muddy River (a tributary of the Quinnipiac River), at which point the road becomes known as Maple Avenue. Maple Avenue runs through some residential areas of North Haven towards the town center. At the town center, Route 103 meets with Broadway (State Road 729), a former alignment of Route 22 and U.S. Route 5. North of Broadway, the road is now known as Washington Avenue, which ends at the junction of Route 5 and 22 after another . Route 103 runs parallel to I-91 between exits 8 and 11.
