The northern terminus is at PA 50 on the border of Green Tree and the Pittsburgh neighborhood of Westwood.

The road passes through residential and commercial areas as it turns to the northeast, narrowing to two lanes as it enters the borough of Green Tree.

In this area, the route passes more homes, with the Blue Belt joining the road at the Potomac Avenue intersection.

The route turns north onto two-lane Poplar Street and heads into wooded areas of homes.

[2][3] The original PA 121 ran from East Waynesburg to Point Marion in Greene County from 1928 to 1950.