12.2 Off-System Bridge Replacement and Rehabilitation Projects (Low-Volume)

12.2.1 Overview

This section provides design guidance for projects meeting all 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; and
  • Current ADT of 400 or less.
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 and corresponding design criteria 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 4
.

12.2.2 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.
  • 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, Nominal Face to Nominal Face of Rail:
     A minimum width of 24-ft may be used when ALL following conditions apply:
    • Approach roadway width is 24-ft or less;
    • The county or local entity has no near-term plans to widen the approach roadway; and
    • There is no major near-term development anticipated.
    If any of the conditions above are not met, a minimum width of 28-ft is required. If the existing approach roadway width is greater than 28-ft then the existing approach roadway width would apply.
  • Bridge End Guard Fence:
    • Minimum Conditions – Transition consistent with current applicable Roadway Design Standards.
    • 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.
  • Approach Roadway Width:
    • For minimum length of 50-ft adjacent to the bridge end, the approach roadway width should match the clear roadway width across the structure plus additional width to accommodate approach guard fence.
    • An appropriate transition (minimum length 50-ft) to the existing roadway width should be made in the sections of approach roadway located at the federal project extremities.
    • If roadway surfacing is included, a minimum roadway width should be used for the 50-ft roadway section adjacent to the bridge.
  • Traffic Control:
    • When provided, and to the extent feasible, detours should, at a minimum, match existing 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
      TMUTCD
      , and details should be included in the plans.
    • See
      Chapter 23
      for more information.