I am looking for the minimum overpass clearance that a driver can
expect when traveling US freeways.

This might complete this statement: "As long as your vehicle and
trailer is shorter than ____ feet/inches, then you don't have to worry
about fitting under bridges on the highway"

thank you!

Hello Phoradan,


The minimum vertical clearance on highways is 16 feet. 


Minimum Vertical Clearance

?Clear height of structures shall not be less than 16 feet over the
entire roadway and usable shoulder width. There shall be an additional
6 inch allowance for future resurfacing on new structures. The
vertical clearance to pedestrian overpasses and sign trusses shall be
minimum 17 feet. The vertical clearance from the bridge deck to cross
bracing on through trusses shall also be minimum 17 feet.?

DD-601
GEOMETRIC DESIGN CRITERIA FOR RURAL HIGHWAYS
September 1, 2003 
West Virginia Department of Transportation
Division of Highways Design Directive
http://www.wvdot.com/engineering/files/600/DD601.pdf


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VERTICAL CLEARANCE ON THE INTERSTATE SYSTEM
4.9 meters (16 feet)

?It must be emphasized that the integrity of the Interstate System for
national defense purposes be maintained to meet AASHTO Policy as
stated in A Policy on Design Standards - Interstate System,
incorporated by reference in 23 CFR 625. On Interstate sections in
rural areas, the clear height of structures shall be not less than 4.9
meters (16 feet) over the entire roadway width, including the usable
width of shoulder. On Interstate sections in urban areas, the
4.9-meter (16-foot) clearance shall apply to a single routing. On
other Interstate urban routes, the clear height of structures shall be
not less than 4.3 meters (14 feet). Design exceptions must be approved
whenever these criteria are not met.?

United States Department of Transportation - Federal Highway Administration
http://wwwcf.fhwa.dot.gov/legsregs/directives/fapg/0625sup.htm


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Standards for Interstate Highways are defined by the American
Association of State Highway and Transportation Officials (AASHTO) in
the publication A Policy on Design Standards - Interstate System.

Vertical clearance

?Minimum vertical clearance under overhead structures (including over
the paved shoulders) of 16 ft (4.9 m) in rural areas and 14 ft (4.3 m)
in urban areas, with allowances for extra layers of pavement. Through
urban areas at least one routing should have 16 ft (4.9 m) clearances.
Sign supports and pedestrian overpasses must be at least 17 ft (5.1 m)
above the road, except on urban routes with lesser clearance, where
they should be at least 1 ft (0.3 m) higher than other objects.
Vertical clearance on through truss bridges is to be at least 17 ft
(5.1 m).?
http://en.wikipedia.org/wiki/Interstate_Highway_standards

AASHTO 
http://transportation.org/aashto/home.nsf/FrontPage

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Search terms:
Minimum vertical clearance highways


I hope the information provided is helpful!

Best regards,
Bobbie7

just what i was looking for.  thank you!

While the above-cited rules may now be in effect (such that any new
structures conform to those rules), there are several overpasses
throughout the US that have clearances less than 14 ft.  A list of
those overpasses can be found here:

http://www.aitaonline.com/Info/Low%20Clearances.html

Many of the overpasses listed here have clearances of 12-13 ft., with
some under 10 ft.  While many of the listings are for non-freeway
roads (i.e. US routes and state and county highways), there are some
listings for low clearances of bridges crossing over interstates.