Chapter 6: Special Facilities

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Section 1: Off-System Bridge Replacement and Rehabilitation Projects

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Project Conditions

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

  • included in the off-system bridge replacement and rehabilitation program
  • facility not likely to be added to the designated state highway system
  • current ADT of 400 or less.

If all the above conditions are not met, then the design criteria for the appropriate class of highway should be utilized. For off-system bridge projects, current ADT may be used with the appropriate 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 the Bridge Project Development Manual.

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Design Values

Design values selected for a particular project should 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 should be used.

  • Minimum Design Speed: Meet or improve conditions that are typical on the remainder of the roadway.
  • Vertical Curvature, Minimum K values: Meet or improve conditions that are typical on the remainder of the roadway.
  • Horizontal Curvature: Meet or improve conditions that are typical on the remainder of the roadway.
  • Minimum Superelevation: Meet or improve conditions that are typical on the remainder of the roadway.
  • Maximum Grades: Meet or improve conditions that are typical on the remainder of the roadway.
  • Minimum Structure Width, Face to Face of Rail: 24 ft [7.2 m].
  • Bridge End Guard Fence:
    • Minimum Conditions – Transition section plus end treatment.
    • If an intervening roadway or driveway prevents usual placement of guard fence, a guard fence radius may be used provided the approach represents a low speed condition.
  • Approach Roadway:
    • For minimum length of 50 feet [15 m] adjacent to the bridge end, the roadway crown should match clear width across structure (24 feet [7.2 m]) plus additional width to accommodate approach guard fence.
    • An appropriate transition (minimum length 50 feet [15 m]) to county road width should be made in the sections of approach roadway located at the federal project extremities.
    • If roadway surfacing is included, a minimum of 20 feet [6 m] surfacing width should be used for the 50 feet [15 m] roadway section adjacent to the bridge.
  • Traffic Control:
    • When provided, and to the extent practical, detours should match existing county road design features. Design details for detours should be shown in the plans and on the preliminary layouts.
    • Traffic control devices should be in conformance with the Texas Manual on Uniform Traffic Control Devices, and details should be included in the plans.
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