Minimum vertical clearance measurements apply to the total travel way, which includes the travel lanes and any usable paved shoulder. A usable shoulder is defined as a paved surface adjacent to and flush with the travel lanes for which the minimum measured clearance is not less than 10 feet. Where a paved shoulder, or section of paved shoulder, passes beneath an overhead obstruction with a minimum vertical clearance less than 10 feet, the installation of a positive barrier should be considered as an additional roadside safety treatment (see Figure 6-2). An elevated paved shoulder at the edge of the travel lanes is not included in clearance measurements. Similarly, raised medians are not considered part of the travel way.

A sufficient number of measurements should be taken across the width and depth of the obstruction to ensure that the minimum clearance is determined. Measurements should be rounded down to the lowest whole inch.