Section 5: Measuring Vertical Clearance

Measuring Vertical Clearance

All vertical clearance measurements of grade separation structures should be verified at least once a year. The measurements taken for “Actual Clearance,” “Signed Clearance,” type of work performed and when it was done should be reported to the Department of Motor Vehicles and the district bridge inspection coordinator.
Sections 621.207
and
621.504
of the Texas Transportation Code restrict a vehicle and its load to a height of no more than 14 feet, unless an oversize/overweight permit is obtained from the department. It is unlawful to operate a vehicle over or on any bridge or through any underpass or similar structure unless the height of the vehicle, including its load, is less than the vertical clearance of the structure as shown by the department's records.

Clearance Determination

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.

Requirements for New Measurements

Any condition which results in a change to the vertical clearance of a structure such as an overlay or reconstruction of the roadway will require new measurements and resubmission of the “Actual Clearance” and “Signed Clearance” to the Department of Motor Vehicles and the district bridge inspection coordinator.
Refer to the
Sign Guidelines and Applications Manual,
 Chapter 6, “Warning Signs,”
Section 3 “Vertical Clearance
,” for information concerning the actual minimum measured vertical clearance.

Signs

Clearance signs need to reflect the vertical clearance between the roadway and the overhead obstruction. Refer to the for specific information on signing criteria of the travel lane and shoulder clearances. The district should notify the Department of Motor Vehicles before traffic is allowed to pass under the obstruction.