Buffalo area US 20A separates from US 20 just northeast of an intersection locally known as "Seven Corners" in the town of
Hamburg. The route heads east through the
Buffalo suburbs on Big Tree Road, entering the town of
Orchard Park and passing south of the southern campus of
SUNY Erie. At Abbott Road, US 20A becomes the "Timothy J. Russert Highway", named for
Buffalo native
Tim Russert. and now part of
CR 356. Past the hamlet, US 20A deviates from its linear east–west alignment, swerving to the south on a newer routing of Big Tree Road before reuniting with its original routing to the east. ahead, US 20A exits Erie County and enters the equally rural
Wyoming County town of
Sheldon. In Sheldon, US 20A intersects
NY 77 near Sheldon Center and
NY 98 in
Varysburg, forming a concurrency with the latter into the adjacent town of
Orangeville. Upon crossing the town line, the two routes split, with NY 98 proceeding southwest to
Java. US 20A continues southeast from NY 98 on a linear alignment, intersecting the southern terminus of
NY 238 at Halls Corner, a small hamlet located near the Orangeville–
Warsaw town line. Shortly after passing NY 238, US 20A makes a turn to the east as it enters Warsaw. Roughly from the town line, US 20A descends into the Oatka Valley, a large ravine containing
Oatka Creek and the entirety of the
Warsaw. Now named Buffalo Street, US 20A heads east–west across the village, intersecting
NY 19, one of two state routes to directly connect
Lake Ontario with the
Pennsylvania state line, at the center of Warsaw. Past the NY 19 junction, US 20A continues east along Buffalo Street to the eastern edge of the village and the valley, where the route turns a full 90 degrees to the north to climb the side of the Oatka Valley. The route ascends approximately , passing under the
Rochester and Southern Railroad (RSR)—which runs along the foot of the gorge—before exiting the valley and returning to an east–west alignment as it heads toward
Perry and points east. All oversize trucks are prohibited from using the section of US 20A between NY 19 and Minor Road at the top of the valley due to the steep grade of the hill and the sharp curve at the bottom.
Warsaw to Geneseo Outside of the Oatka Valley, US 20A heads east through the remainder of the town of Warsaw prior to entering the town of Perry. The route serves
Perry–Warsaw Airport on its way to Perry Center, a small hamlet situated directly north of the village of
Perry, where US 20A intersects
NY 246. The portion of US 20A in Perry is otherwise uneventful, and the route quietly passes into the
Livingston County town of
Leicester later. After another of rural surroundings, US 20A meets
NY 39 at a junction approximately southwest of the village of
Leicester. The two routes converge, following Leicester Road northeast to the village, where the highway's name shifts to Main Street upon entering the village limits. East of a
grade crossing with the
Genesee and Wyoming Railroad subdivision of the RSR, US 20A and NY 39 connect to
NY 36 at York Road. NY 36 briefly overlaps with US 20A and NY 39 for one block before heading to the south via Mount Morris Road at the village center. US 20A and NY 39 continue on, leaving Leicester on as Cuylerville Road, named for
the community located directly northeast of Leicester. The routes pass in and out of Cuylerville and head eastward into a wide valley, crossing Beards Creek and the
Genesee River. At the eastern bank of the latter, the highway crosses into the town of
Geneseo. On the other side of the Genesee River, US 20A and NY 39 rise in elevation once more as they head to the northeast, climbing the eastern edge of the gully to meet
NY 63 at the valley's eastern edge. After a brief concurrency with US 20A and NY 39, NY 63 splits off to the west, running alongside the western edge of the nearby
State University of New York at Geneseo campus. In contrast, US 20A and NY 39 form a portion of the eastern edge of the campus between NY 63 and
Mary Jemison Drive in the village of
Geneseo. At the latter intersection, US 20A and NY 39 turn east onto South Street. After just one block, the US 20A/NY 39 overlap comes to an end as NY 39 follows Main Street north out of Geneseo toward
Avon. US 20A continues east through Geneseo before taking on a more northeasterly alignment outside of the village. At this point, the highway becomes Lakeville Road for the
Conesus Lake community to the northeast. The route proceeds across open terrain to the western outskirts of
Lakeville, where US 20A connects to
I-390 at exit 8. Past the expressway, US 20A continues on a northeast alignment—albeit more eastern than northern—as it intersects
NY 256 and enters both the town of
Livonia and the hamlet of Lakeville.
Finger Lakes As Big Tree Road once more, US 20A acts as the major east–west thoroughfare for Lakeville, connecting the hamlet to I-390 in the west to the village of
Livonia to the east. In the center of Lakeville, US 20A intersects the north–south
NY 15. The two routes converge on Big Tree Road, following the roadway around the northern tip of Conesus Lake and southeastward through the rural landscape between Lakeville and Livonia. In Livonia, Big Tree Road continues to the southeast as Big Tree Street; however, US 20A and NY 15 leave Big Tree Road to follow Main Street instead. NY 15 remains on US 20A for one more block to the center of Livonia, at which point it continues southward on Commercial Street toward
Conesus while US 20A heads east on Main Street and out of the village as Richmond Mills Road. For the next , US 20A loosely parallels Big Tree Road, located about to the south. At a rural junction known as Bosley Corner, US 20A merges with the north–south
NY 15A and follows NY 15A south toward the hamlet of
Hemlock. While concurrent with NY 15A, US 20A crosses Big Tree Road at the midpoint of the concurrency. The two routes proceed through Hemlock before splitting south of the community. Here, US 20A breaks from NY 15A and continues east on Honeoye Road into the
Ontario County town of
Richmond. About into the sparsely developed town, US 20A reconnects to Big Tree Road at Curtis Corner. The route, however, becomes Main Street for the hamlet of
Honeoye a short distance to the east. US 20A runs east–west through the small yet highly developed community, crossing
Honeoye Creek and passing north of
Honeoye Lake. It leaves the hamlet soon after, turning to the northeast and traversing a series of small hills as it passes into the town of
Bristol as Honeoye Road once again. Roughly from the town line, US 20A intersects
NY 64 in the
Bristol Valley. US 20A turns north onto NY 64, following the state route out of the valley and into the town of
East Bloomfield, where US 20A ends later at an intersection with US 20 and NY 5. The section of US 20A that overlaps NY 64 was signed north–south, matching NY 64's direction, however, the US 20A north–south tabs were replaced by east–west tabs between 2010 and 2012, but still the north–south tabs are now for NY 64 shields only. NY 64 continues west from the junction on US 20 and NY 5. ==History==