The freeway also serves several smaller communities between Corning and Rochester, including the Livingston County villages of Dansville and Geneseo.

From Lakeville north to Brighton, the two routes cross paths four times and are located no more than 1.5 miles (2.4 km) apart along the entire stretch.

More sections of the freeway opened throughout the 1970s, and I-390 was extended northwestward to cover the southwestern quadrant of the Rochester Outer Loop in 1980 following the elimination of NY 47.

In its southern sections, which account for most of the highway's mileage, I-390 is a lightly trafficked freeway of two lanes in either direction going through minimally populated rural areas.

I-390 climbs gradually as it continues past Cohocton, eventually turning due west as it descends to an interchange with NY 21 south of Wayland.

[5] The road climbs again as it makes a gentle bend and widens as it crosses the Livingston County line just south of Dansville and north of Stony Brook State Park.

North of the village, it climbs to the west side of the wide valley of Canaseraga Creek, giving the roadway a view over the area known locally as the Flats.

At this point, the highway follows more level ground, with woods and swamps mostly replacing farmland in the surrounding landscape.

[4] After passing rest areas on either side, I-390 reaches the NY 408 exit adjacent to the American Rock Salt mine at Hampton Corners.

Here, most traffic bound for the Buffalo area exits to go west to Mount Morris, visible across the Flats from the freeway, where it follows NY 36 north.

A mile (1.6 km) north of the exit, Canaseraga Creek drains into the Genesee River on the road's west side.

[4] For the next mile (1.6 km), I-390 follows a more northwesterly alignment along the northeastern edge of the Greater Rochester International Airport grounds.

In one proposal submitted to the American Association of State Highway and Transportation Officials in the late 1970s, I-590 would be truncated to begin at the then-proposed junction with I-390 in Brighton.

[14] On February 10, 2008, whiteout conditions caused a 36-car pileup near the Scottsville Road exit, which led to a 17-year-old girl's death.

[20] On July 17, 2011, a tour bus heading northbound from Washington DC to Niagara Falls crashed between the Avoca and Cohocton exits, killing two and injuring at least 35 others.