Maryland highway officials committed to avoid a historical African American cemetery when adding toll lanes to the Capital Beltway after 27 “probable” or “possible” unmarked graves were detected along the highway this summer, a state archaeologist said Thursday.

The potential for graves atop a grassy embankment along the Beltway’s Inner Loop prompted state officials to shift the project’s “limits of disturbance” to spare the area, said Julie M. Schablitsky, chief archaeologist for the Maryland Department of Transportation. The sites are on the highway side of a chain-link fence between the Beltway and Moses Morningstar Cemetery in Cabin John.

“We don’t know with 100 percent certainty that’s what they are,” Schablitsky said. “But the patterns give enough indication that it’s probably a cemetery area, and we need to avoid it.”