Vertical clearance determination should apply to the total travelway, which includes the travel lanes and any usable paved shoulders. 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 rolled curb or elevated shoulder exists, clearances should not include the shoulder area. Where a flush shoulder exists (with or without jiggle bars,) the clearance determination should include the shoulder area.

A sufficient number of measurements should be taken to ensure the critical clearance is determined. In locations where an encroachment over the usable shoulder would significantly reduce the vertical clearance, two clearances may be shown. The travel lane and shoulder clearances should be signed independently on the structure.