4.8.6 Vertical Clearance

Minimum vertical clearance for structures should be calculated from the point on the roadway with least clearance including the outside edge of one shoulder to the other. This includes both sides of the structure being passed under to verify all vehicles can clear the structure at any point along the structure including travel lanes and shoulders.
Required vertical clearances also allow for potential future overlays.
Table 4-13
shows the minimum vertical clearances required.
Section 21.2
provides additional guidance for roadways on the THFN.
See
Chapter 1
for additional information on vertical clearance design exceptions, and THFN design deviations.
During construction, refer to TxDOT’s
Bridge Design Manual - LRFD
for requirements on maximum time between erection of girders and placement of deck for spans overactive lanes of traffic to avoid over-height impacts.
At a minimum, during construction, bridge vertical clearances and all other obstructions above traffic, including temporary works, must be 14.5-ft.
A clearance of 15-ft is preferable to provide a sufficient buffer between allowed and actual heights to avoid over-height impacts.
Table 4-13: Vertical Clearance Requirements1
Functional Classification
Vehicle Overpasses
2
(ft)
Overhead Sign Structures
and Bicycle / Pedestrian
Overpasses
4
(ft)
Local/Collector/Arterial
16.5
3
17.5
Freeway
16.5
17.5
Texas Highway Freight Network (THFN)
5
18.5
19.5
Notes:
  1. Vertical clearance requirements include an additional 0.5-ft. to accommodate future resurfacing as required by AASHTO’s A Policy on Geometric Design of Highways and Streets.
  2. Intersecting roadway goes over the functionally classified roadway.
  3. Exceptional cases near as practical to 16.5-ft but never less than 14.5-ft.
  4. Includes overhead signs, light fixtures, sign bridges, and toll gantries.
  5. If an overlay reduces the vertical clearance below 18.0-ft, a THFN Design Deviation will be required.