The
Inland Empire Highway was originally a collection of gravel
county roads that have existed since 1898 in the
Spokane area and 1905 in the
Pullman area. These roads roughly followed an early territorial highway built in the 1870s between Colfax and Spokane. The highway was added to the state highway system in 1913, traveling within the
Palouse region between
Colfax and Spokane. The
Second Division of the Eastern Route of the Inland Empire Highway was also established in 1913, traveling northwest from
Sampson Trail Y at the
Idaho–
Washington state line to
Pullman. The Idaho portion of US 195 became part of the North and South Highway in 1916 and was not numbered under Idaho's state highway system in 1953. The gap in the Second Division between Pullman and Colfax was named by
Whitman County as a highway of importance the following year and was not built until 1925 as part of State Road 3.
State Road 23, connecting Spokane to
Newport, was designated in 1915 before it was renamed to the
Pend O'Reille Highway and renumbered to
State Road 6 in 1923. The Inland Empire Highway was numbered as
State Road 3 in 1923 and retained the designation as
PSH 3 in 1937, while State Road 6 became
PSH 6. The
United States Highway System was established on November 11, 1926, during its adoption by the
American Association of State Highway Officials (AASHO) and included US 195, traveling north from
US 95 within Washington through Pullman and Spokane before ending at
US 95 in
Sandpoint, Idaho. The present four-lane
divided highway along
Hangman Creek in
Spokane was constructed in 1939 as part of general improvements to
Eastern Washington highways, relocating the route of the creek and a nearby
Northern Pacific Railway line. The section of US 195 between Spokane and Sandpoint became co-signed with an extension of
US 2 from
Bonners Ferry, Idaho to
Everett, Washington in 1946, and the highway was truncated to
US 10 and
US 395 in 1969. During the
1964 highway renumbering, Washington converted its highways to the present state route system, to take effect in 1970. US 195 replaced PSH 3 and its branches along its present route, with its southern terminus at US 95 atop Lewiston Hill in Idaho and its northern terminus at
I-90 in Spokane at an interchange that was opened in December 1965, along with a new segment between Thornton and
Rosalia. Between 1973 and 1975,
State Department of Highways completed construction of three highway bypasses around Pullman, Rosalia, and Plaza. Funds that were originally intended for the canceled
Bay Freeway project in
Seattle were instead redirected to the bypasses earlier in the decade. A four-lane bypass of Colfax was approved for construction in 1971, but deferred indefinitely due to a lack of funding. The western bypass of Pullman was completed in 1974 at a cost of $1.04 million. The highway between
Uniontown and Rosalia was designated as part of the
Palouse Scenic Byway on December 19, 2002, as part of the
Washington State Scenic and Recreational Highways program. In 2002, WSDOT adopted a long range plan to upgrade US 195 within the Hangman Valley in Spokane to
limited-access standards by constructing new interchanges at four intersections. One of the interchanges, at Cheney–Spokane Road, was completed in 2014 at a cost of $9.4 million. Funding for the remaining interchange projects, estimated to cost $106 million in 2002 dollars, was not allocated and WSDOT is instead considering lower-cost improvements to the intersections. Increased traffic congestion on US 195 in Spokane lead to a development moratorium in place until capacity improvements are made to the highway. The first
ramp meter in the Spokane area was installed at US 195's interchange with I-90 in 2019. ==Major junctions==