Chapter 6: Special Facilities

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Section 1: Off-System Bridge Replacement and Rehabilitation Projects

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Overview

This section provides design guidance for projects meeting all the following conditions:

If all the above conditions are not met, then the design criteria for the appropriate functional class of highway should be utilized. For off-system bridge projects, current ADT may be used with the appropriate functional class of highway (i.e., enter tables, charts, or figures with current ADT substituted for future ADT). Where significant traffic growth is expected or the roadway will be widened in the near future, the use of future ADT for design purposes is encouraged.

For more information on the off-system bridge replacement and rehabilitation program, refer to TxDOT’s Bridge Project Development Manual.

Additional vertical clearance requirements may apply to bridge projects on the Texas Highway Freight Network (THFN) as specified in Chapter 3, Section 8.

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Design Values

Design values selected for a particular project must satisfy and preferably exceed the values shown below. Selected design values should be consistent and compatible with the prevalent design features on the existing off-system roadway. If the route has the potential for significant ADT increases in the near future, or if the character of the traffic is not local, design requirements for the appropriate class of highway must be used.

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  • Minimum Design Speed: Meet or improve conditions that are typical on the remainder of the roadway.
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  • Vertical Curvature, Minimum K values: Meet or improve conditions that are typical on the remainder of the roadway.
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  • Horizontal Curvature: Meet or improve conditions that are typical on the remainder of the roadway.
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  • Minimum Superelevation: Meet or improve conditions that are typical on the remainder of the roadway.
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  • Maximum Grades: Meet or improve conditions that are typical on the remainder of the roadway.
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  • Minimum Structure Width, Face to Face of Rail: 24-ft. for approach roadway widths of 24-ft. or less. 28-ft. is the minimum if the approach roadway is over 24-ft. in width, or the county or municipal entity has near term plans to widen the approach roadway, or anticipates near term development.
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  • Bridge End Guard Fence:
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    • Minimum Conditions – Transition consistent with current applicable Roadway Design Standards.
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    • If an intervening roadway or driveway prevents usual placement of guard fence, a guard fence radius may be used consistent with specific application in the applicable Roadway Design Standard.
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  • Approach Roadway:
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    • For minimum length of 50-ft adjacent to the bridge end, the roadway crown should match clear width across structure plus additional width to accommodate approach guard fence.
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    • An appropriate transition (minimum length 50-ft) to county road width should be made in the sections of approach roadway located at the federal project extremities.
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    • If roadway surfacing is included, a minimum of the bridge roadway width should be used for the 50-ft roadway section adjacent to the bridge.
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  • Traffic Control:
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    • When provided, and to the extent feasible, detours should at a minimum match existing county road design features. Design details for detours should be shown in the plans and on the preliminary layouts.
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    • Traffic control devices should be in conformance with the Texas MUTCD, and details should be included in the plans.
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