The boulevard was first proposed in 1913 in order to alleviate traffic on
Bigelow Boulevard (then known as Grant Boulevard), which was a major, though not very direct, route for automobile traffic between
Downtown,
Oakland, and
Schenley Park. The proposed route, carved out of the
Bluff above the
Monongahela River, would connect the same areas over a distance about shorter. Like Pittsburgh's other boulevards, the new route would be off-limits to streetcars, wagons, and other slow-moving vehicles. In 1919, the
Pittsburgh City Council selected "Boulevard of the Allies" as the name of the proposed roadway, previously known as Monongahela Boulevard. , shortly after completion in 1922 Work began with the widening of Second Avenue to a width of 70 feet (20 m) between
Liberty Avenue and
Grant Street in 1920–21. The boulevard itself was built on an elevated viaduct beginning at Second Avenue and Grant Street and climbing over the
Panhandle Route tracks onto the Bluff, where the roadway then followed the cliff edge eastward to Oakland. The project was an engineering challenge requiring extensive grading and numerous retaining walls and viaducts. Prior to completion, the cost was reported as $1.6 million per mile, said to be the most expensive road in the world at the time. The first section of the boulevard from Downtown to the intersection with
Forbes Avenue at the edge of West Oakland opened on October 2, 1922, and was formally dedicated a month later on
Armistice Day. The remainder of the route, extending to Schenley Park partly along the existing Emily and Wilmot Streets, was completed in 1930. In 1923, an experimental synchronized
traffic signal system which allowed a central operator to coordinate signal changes at multiple intersections was tested on the downtown section of the Boulevard. Another novel system was installed in 1931 which signaled a protected left turn automatically when a turning vehicle was detected. In 1924, the Boulevard became part of an alternate
bypass route of the
Lincoln Highway, whose original route used Bigelow Boulevard into downtown; this left the Boulevard at
Forbes Avenue (its original terminus), following Beeler Street, Wilkins Avenue, and Dallas Avenue to the main route on
Penn Avenue near
East Liberty. The Boulevard at
Grant Street was once home to Pittsburgh's
Chinatown until the 1950s.
U.S. Route 22 and
U.S. Route 30 were designated along the
William Penn and Lincoln Highways through Pittsburgh in 1926; the Boulevard of the Allies bypass alignment was chosen for both routes. The portion of the road east from Forbes Avenue to Bates Street, still known as Wilmot Street, became a part of
Pennsylvania Route 885 by 1940. With the completion of the
Penn-Lincoln Parkway East in the late 1950s, US 22 and US 30 were moved off the Boulevard, and PA 885 was extended west a short distance to the interchange near the
Birmingham Bridge. The construction of
I-579 in the early 1960s cut the path of westbound Boulevard traffic into downtown; eventually the PA 885 designation was continued west to this interchange. == Major junctions ==