4.4.5 Structures

The location of proposed bridges must be determined early in project development. Characteristics such as limits of bridge, bent locations, and span type and lengths of bridges crossing water can usually be set with strong certainty early in project development. Planning for overpasses, underpasses and interchanges requires an iterative process to satisfy structural capability and horizontal and vertical clearance requirements between roadways and bridges.
Culverts with a total span greater than or equal to 20 feet are considered bridge-class culverts and their design must follow span bridge guidelines.
Bridge layouts can be created once horizontal/vertical alignments, typical sections and drainage design are developed. The bridge layouts are sent to the District and BRG for review. This submission is referred to as the Preliminary Bridge Layout Review (PBLR) and it typically occurs between the Initial (30%) and Detailed (60%) plans milestones (refer to the
PS&E Preparation Manual
 and the
Bridge Project Development Manual
 for more details). Accommodations for future bridge widening should be considered during the preliminary planning. Preliminary bridge layout reviews include bridge class culverts.
If the project is on or near railroad ROW, the RRD will coordinate with the specific railroad. Refer to the TxDOT.gov Railroad Design Guidelines webpage for details on design, coordination and agreements required for specific railroads.
Considerations in the preliminary planning for bridges include:
  • Identify applicable Federal Emergency Management Agency (FEMA), U.S. Corps of Engineers (COE) and U.S. Coast Guard (USCG) constraints, studies required, and coordination and permits required;
  • Review railroad requirements and coordinate with RRD for railroad crossings;
  • Identify and determine historic age considerations and constraints;
  • Identify hazardous materials issues and abatement requirements;
  • Identify type, size, and location of existing and proposed bridges and document in the DSR;
  • Determine vertical and horizontal clearance requirements;
  • Identify utilities that will need to be removed from the existing bridge prior to construction;
  • Identify potential conflicts with foundations, including existing foundations or subsurface utilities – obtain as-built plans from all structures previously constructed to determine locations of buried foundations;
  • Determine load rating for bridge widening and obtain condition survey;
  • Consider rehabilitation and widening of the existing structure versus replacement;
  • Review proposed bridge cross sections with local public agency or railroad company when grade separation structures involve facilities not owned or maintained by TxDOT; and
  • Coordinate with District TP&D to determine if Advanced Funding Agreement is in place, if applicable.
Coordinate with the District Bridge Engineer to determine District specific PBLR submission requirements. Detailed bridge design should not begin prior to approval of the PBLR.
4.4.5.2 Retaining/Sound Walls
Preliminary retaining wall locations are established as part of developing the geometric schematic. Preliminary sound wall locations are established based on the traffic noise analysis. Retaining wall or sound wall locations may be revised as the project development progresses.
4.4.5.2.1 Sound Walls
A sound wall is a structure designed and constructed to reduce the impact of traffic-related noise on nearby communities and sensitive areas. A noise study analysis must be performed to determine where noise impacts are predicted and will determine recommendations for placement of sound walls.
Considerations in the placement of sound walls include:
  • Refer to the traffic noise analysis for the location and dimensions of the proposed sound wall;
  • Determine if aesthetics are to be included as this will affect the design. For sound walls adjacent to residential areas and parklands, aesthetics may play an important role in developing the wall. Coordinate with planners, landscape architects and community groups early in project development;
  • The placement of the sound wall often depends on existing or proposed utility lines. Coordinate early with utility owners to determine locations of existing and proposed lines;
  • Determine if a berm may be effectively used to mitigate noise. It may be used with a sound wall barrier and allow for a shorter, more aesthetically pleasing wall;
  • Evaluate the need for future access to adjacent property and potential openings in the wall; and
  • Determine if placement of the sound wall can be made within the existing ROW (consider the design and construction of the wall footing) or if additional ROW or permanent easements are needed.
Locating retaining walls and/or sound walls will assist in determining locations of needed soil core borings for foundation design.
4.4.5.2.2 Retaining Walls
A retaining wall is a structure designed and constructed to resist the lateral pressure of soil. TxDOT divides retaining walls into permanent and temporary walls. A permanent retaining wall is designed to have a service life of 75 years, while a temporary wall has a service life of 3 years.
Considerations in the placement of retaining walls include:
  • Compare retaining wall cost to bridge cost to determine height at which bridge is more cost effective (typically at 20-ft height, bridge structure becomes more feasible);
  • Determine if the retaining wall also needs to act as a sound wall;
  • Determine if the retaining wall will be supporting traffic lanes. If so, the design must account for traffic loading and barrier affect loading;
  • Check sight distance for walls in cut sections at intersecting streets and driveways;
  • Determine if street lights, overhead bridge signs, concrete traffic barriers, or traffic signs will be attached to the wall;
  • Consider width of retaining wall base during construction and placement near ROW line (buried portions of permanent structures cannot be placed outside of the ROW line);
  • Ensure adequate clear zone between travel lanes and the retaining wall is provided; and
  • Do not place the retaining wall in a gore area.