MD 198 begins at a four-legged intersection with MD 650 (New Hampshire Avenue) west of Spencerville. The west leg of the intersection is county-maintained Norbeck Road, which leads west to MD 28. MD 198 heads east as two-lane undivided Spencerville Road through an intersection with Good Hope Road and passes through the village of Spencerville. At the western edge of Burtonsville, the highway expands to a four-lane undivided highway and has a three-way intersection with Old Columbia Pike and takes on that name. MD 198 expands to a six-lane divided highway just west of its three-quarter diamond interchange with US 29 (Columbia Pike). Access from southbound US 29 to MD 198 is provided via Old Columbia Pike, a bypassed segment of US 29 that intersects MD 198 opposite the ramp from MD 198 to southbound US 29.