Before 1980 KY 80's original western terminus was located near
Bristow, just east of Bowling Green from its 1929 establishment through the early 1950s; the segment from Columbus to US 68 in Aurora was originally signed as
KY 98. In the late 1940s, when US 68 was rerouted to its current routing between Bowling Green and Perryville, KY 80's western terminus was truncated to its junction with US 68 in Edmonton. KY 80 was extended to its late-20th century length, including the concurrency with US 68, at sometime in 1954. From around 1948 through 1952, Russell S. Dyche, an editor for the
London Sentinel-Echo, led a years-long effort to persuade the Kentucky Department of Highways (now the
Kentucky Transportation Cabinet) to extend the KY 80 designation westward onto its route from Edmonton to Columbus, including the US 68 concurrency. Dyche, who also led a motorcade to KY 80's current western terminus all the way from Elkhorn City, continued to promote the highway until his late 1959 death. In 1978, the segment of KY 80 from Somerset to London was named the Russell Dyche Memorial Highway.
Columbus–Belmont ferry Originally, KY 80 continued westward via a ferry crossing of the
Mississippi River to
Belmont, Missouri, where it continued westward as
Missouri Route 80, which travels west to
US 61/
US 62 (and
I-55 in the present day) between
New Madrid and
Sikeston, Missouri. The toll ferry service was discontinued in 1984.
Proposed Interstate 66 in the Daniel Boone National Forest The state's
I-66 proposals called for KY 80 to be bypassed in the area between Somerset and London, with the new road to share only the crossing over the
Rockcastle River gorge. This proposal has met with controversy in the mid-2000s, with area residents preferring that the new Interstate be built on the existing KY 80 right of way. The project has since lost interest.
Late 20th century realignments KY 80's original alignments in
Knott and
Perry counties were renumbered to
KY 550 at some point around 1979–1980. Several other segments of KY 80 were rerouted in various areas between Somerset and Prestonsburg between 1977 and 1984.
Widening project in south-central Kentucky When the US 68/KY 80 four-lane realignment between Hopkinsville and Bowling Green was completed in the late 1990s, several of the route's old alignments were kept intact, notably in areas between Hopkinsville and Bowling Green. As new four-lane segments were completed, old alignments of US 68/KY 80 in Fairview, Elkton, Russellville, and Auburn were converted into
business routes of US 68 as the widening project continued. Sometime in 2007, the route was rerouted onto a bypass route around Cadiz; the original alignment in that city also became a US 68 business loop. In the early 2010s, US 68 and KY 80's alignment in Bowling Green would eventually be rerouted on Veterans Memorial Boulevard. The highway's Glasgow alignment was rerouted onto much of the
Veterans Outer Loop in 2015.
Rerouting in the Purchase area The KY 80 alignment from Brewers to Aurora was renumbered as
KY 402 at some point during the 2002/2003 fiscal year. Around that time, KY 80 was re-routed onto a four-lane highway from Mayfield to Aurora via the northern outskirts of
Murray. The segment from US 641 to US 68 was completed in 2006, while the remainder was built during the 2008/2009 fiscal year.
Eggners Ferry Bridge collapse of 2012 On January 26, 2012, the
Eggner's Ferry Bridge carrying KY 80 and US 68 over
Kentucky Lake (
Tennessee River) near Aurora collapsed because a cargo ship crashed into one of the bridge's support pillars. The bridge re-opened to traffic in May 2012, but it was replaced by a four-lane bridge that was built more than three years afterwards. A new bridge with similar design over Lake Barkley was completed in 2018 to replace the old bridge near Canton. ==Major intersections==