Prior to the U.S. Numbered Highway System, the route was designated as
Route 2 of the
New England road marking system that existed between 1922 and 1927. When US 5 was first commissioned, it took over the entirety of Route 2. In 1927, US 5 had still not been paved in Vermont. Paving in Vermont was completed by 1933.
Connecticut Originally, the route began at the
New Haven Green in downtown
New Haven (at
US 1). Between New Haven and
North Haven, it originally ran east of the
Quinnipiac River along modern-day Middletown Avenue (part of
Route 17) and
Route 103 (the modern alignment was then designated as US 5A). In
Hartford, US 5 passed by
Central Row in the downtown area, entering the city via Maple Avenue and exiting on the
Bulkeley Bridge with
US 6. The southern terminus of US 5 has been realigned several times. By 1938, US 5 bypassed downtown New Haven via the
Prospect Hill,
Dixwell, and
West River neighborhoods, ending at Davenport and Columbus Avenues. In the mid-1950s, US 5 was instead routed through the
Mill River neighborhood ending at East Street and Forbes Avenue. The modern New Haven to North Haven designation was also in place around this time. When
I-91 opened in 1967, the alignment was truncated to its current terminus at exit 5 of I-91.
Massachusetts The
Massachusetts Highway Commission noted in 1912 that between
Longmeadow and
Agawam, the traffic between the
Pioneer Valley and Connecticut was heavier on the east side. The western route from Hartford to
West Springfield, via what is now River Road in Agawam and
Route 159 in Connecticut, was designated
US 5 Alternate. The main route, US 5, was originally designated to run on the east side of the river from Hartford into downtown
Springfield, over the
Memorial Bridge, along Memorial Avenue, up a four-lane Main Street, and then to Park Street (and Park Avenue going in the opposite direction), and up what is now Elm Street, to Riverdale Street. Riverdale Street at that time followed the northern part of the current Elm Street and ended at Witch Path. In 1938, due to congestion in the West Springfield town center, US 5 was moved to a newly constructed bypass from the North End Bridge to East Elm Street, where it continued north along the modern Elm Street and Riverdale Road. In 1941–1942, a four-lane highway was built from East Elm Street to the current Elm Street fork just south of Morgan Road. The designations of both Riverdale Road and US 5 were moved to the new more easterly route. In 1952–1953, construction was started on the modern four-lane highway from the new South End Bridge in Agawam to the existing bypass at the North End Bridge. Tunnels were built under the rotaries at the Memorial and North End bridges so US 5 traffic and local traffic would not intersect. In 1971, the Riverdale Road portion of US 5 was upgraded to a divided highway, with the installation of a steel median, and in 1987–1988, a new lane was added to accommodate the new Riverdale Shops at Daggett Drive.
Vermont US 5 in Vermont mostly followed the Route 2 alignment when it was first designated. Minor deviations from the current route are found in the urban compacts of
White River Junction,
Burke,
Coventry, and
Derby Center. From 1927 to 1929, US 5 was temporarily routed into
New Hampshire along part of what is now
New Hampshire Route 12 between
North Walpole and
Charlestown. The US 5 designation was removed when the road opposite the Connecticut River in Vermont had been improved. In 1931, US 5 in Vermont was taken over by the state, which began paving the road. Over the years a few minor reroutings within populated centers have taken place. The current alignment was in place by 1975. ==Major intersections==