23 CFR § 750.103
Measurements of distance
May 21, 2020
(a) Distance from the edge of a right-of-way shall be measured horizontally along a line normal or perpendicular to the centerline of the highway.
(b) All distances under §750.107 (a)(2) and (b) shall be measured along the centerline of the highway between two vertical planes which are normal or perpendicular to and intersect the centerline of the highway, and which pass through the termini of the measured distance.
[38 FR 16044, June 20, 1973, as amended at 41 FR 9321, Mar. 4, 1976]