As Park Heights Avenue, the state highway is one of two primary radial routes (with MD 140) in the northwestern part of the city, providing access to The Maryland Zoo and Pimlico Race Course.

[1][3] The one-way pair of MD 129 passes between the Upton neighborhood to the southwest and Madison Park to the northeast.

MD 129 passes between the Pimlico neighborhood to the northeast and Arlington to the southwest, then intersects Northern Parkway.

The state highway passes through the affluent Glen neighborhood and between the heavily Jewish neighborhoods of Cross Country to the northeast and Fallstaff to the southwest before intersecting Slade Avenue at the northwest corner of the city of Baltimore, just north of Temple Oheb Shalom.

[1][3] Once in Baltimore County, MD 129 veers north, reduces to two lanes, and passes between the Suburban Park Golf Course to the west and the Dumbarton Historic District on the east.

At the north end of both complexes, the state highway intersects Old Court Road, which heads east as MD 133.

MD 129 passes Druid Ridge Cemetery before temporarily expanding to a four-lane divided highway for its half-diamond interchange with I-695 (Baltimore Beltway).

A short distance north of I-695, MD 129 exits Pikesville and enters a rural area with scattered estate residences.

The state highway crosses Jones Falls and intersects MD 130 west of the hamlet of Stevenson.

[4] Park Heights Avenue was paved from the Baltimore city limits near Cold Spring Lane north to Caves Road by 1910.