Section 3: Horizontal and Vertical Clearances
Anchor: #i1001765Overview
Clearances are established by AASHTO, American Railway Engineering and Maintenance-of-Way Association (AREMA), FHWA, U.S. Army Corps of Engineers, U.S. Coast Guard and, to some extent, local authorities. Minimum horizontal and vertical clearances for highway bridges are established in the TxDOT Roadway Design Manual, repeated in the TxDOT Bridge Project Development Manual, and tabulated here for ready reference. Clearances to railroads are specified by AREMA. Intracoastal canal clearances are determined by the U.S. Army Corps of Engineers. International shipping lane clearances must be negotiated with the U.S. Coast Guard.
Anchor: #i1001782Highway Grade Separations
Clearance measurements for highway grade separations are depicted in Figure 4-2, below. For a complete listing of horizontal and vertical clearances for specific highway functional classifications, see the Roadway Design Manual.
|
Vertical |
14'-6" (4.42 m) |
Absolute minimum |
|---|---|---|
|
|
16'-6" (5.03 m) |
To be provided over all roadways if possible and mandatory for new construction over interstate highways |
|
Horizontal |
1'-6" (0.46 m) |
Absolute minimum from face of curb or barrier |
|
|
10'-0" (3.05 m) |
From edge of travel lane on low-speed, low-volume roadways |
|
|
16'-0" (4.88 m) |
From edge of travel lane on medium-volume roadways and freeway ramps |
|
|
30'-0" (9.14 m) |
From edge of travel lane on high-volume roadways and all freeway main lanes |
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NOTE: Special conditions that would severely increase structure cost may justify negotiation of these clearances with the TxDOT Bridge Division. |
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Stream Crossings
|
Vertical |
2'-0" (0.61 m) |
Desired, above design high water |
|---|---|---|
|
|
1'-0" (0.30 m) |
Absolute minimum, above design high water |
|
Horizontal |
As determined by topography and hydraulics |
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Railroad Overpasses
See Figure 4-2.
|
Vertical |
23'-0" (7.01 m) |
Absolute minimum |
|---|---|---|
|
|
24'-3" (7.39 m) to 26'-0" (7.92 m) |
May be required for electric powered trains |
|
Horizontal |
9'-0" (2.59 m) |
Absolute minimum (12' crash walls required) |
|
|
12'-0" (3.66 m) |
Desirable minimum (6' crash walls required) |
|
|
25'-0" (7.62 m) |
Minimum to eliminate crash walls |
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Railroad Underpasses
|
Vertical |
Same as for Highway Grade Separation Structures |
|---|---|
|
Horizontal |
Same as for Highway Grade Separation Structures |
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NOTE: Although the horizontal clearance criteria for a railroad underpass are the same as for a highway grade separation structure, consideration should be given to using appropriate barrier railing through the railroad underpass, allowing for a reduced horizontal clearance. Given the high cost of this structure type, this practice will greatly reduce bridge cost by reducing the required span length. |
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