Maryland Code, Transportation § 8-732

(1) The centerline of the main traveled way of a nondivided highway; or

(2) A line equidistant from the edges of the median separating the main traveled ways of a divided highway.

(e)(1) For purposes of this subsection, the following rules apply.

(2) Alleys, undeveloped rights-of-way, private roads, and driveways may not be regarded as intersecting highways.

(3) Only highways that enter directly into the main traveled way of the federal-aid primary highway may be regarded as intersecting.

(4) Official and “on premise” signs, as defined in Title 23, § 131(c) of the United States Code, may not be counted, and measurements may not be made from them for purposes of determining compliance with the spacing requirements.

(5) The minimum distance between signs shall be measured along the nearest edge of the pavement between points directly opposite the signs.

(6) The minimum spacing criteria specified in this section do not apply to sign structures separated by a building or other obstruction so that only one sign structure is visible from any one place on the main traveled way.