Minnesota Department of Transportation

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Project development

Engineering process | Scoping

Bridge Design

Purpose

Bridge design is the development of construction plans for bridges and bridge-sized box culverts for transportation projects. Project-specific bridge designs must blend with surface design elements to create a seamless product.

When to use this subject

Any project that has a bridge or bridge-sized box culvert within its limits will require bridge design. Box culverts meet the definition of a bridge when the span perpendicular to the roadway is 10 feet or greater.

For specific process information, see the other guidance page and/or contact the individuals on the contacts page.

How this subject fits into the overall project development process

Bridge work type (replacement, repair, etc) is determined during scoping. Bridge scoping then leads into preliminary design for new or replacement structures. For repair or preservation projects, no preliminary plans are developed. The equivalent for repair and preservation projects is the development of bridge repair recommendations. The recommendations give direction to final design to develop bridge plans. For new or replacement projects, request a new bridge number once the structure type (culvert, bridge) is determined. Structure type is typically determined during the scoping phase.   

Preliminary bridge design

Bridge preliminary design starts in the preliminary design phase. To start preliminary bridge design, the Bridge Preliminary Plans Unit need the following from the district:

  • Bridge surveys (including waterway surveys if over water)
  • Roadway information (alignment, profile, cross section, etc)
  • Other project information

For the preliminary bridge design to be complete and signed, the Bridge Preliminary Plans Unit need a signed layout and final foundation recommendation. The foundation recommendation comes from the Regional Bridge Construction Engineer in the Bridge Office, based on foundation boring information from the Materials Office.  Preliminary bridge plans are typically not developed for box culverts, unless they involve pedestrian underpasses.

Bridge repair recommendation development

Bridge repair recommendations start after bridge scoping and prior to bridge final design. Repair recommendations are the equivalent to preliminary plans for bridge repair and preservation projects. Bridge repair recommendations are developed by the Regional Bridge Construction Engineers, with concurrence from the District Bridge Engineer.

Final bridge design

Bridge final design follows the bridge preliminary design or repair recommendation development phase.  Bridge design must be complete by project turn in.

Box culvert design

Bridge culvert design begins in the final design phase after the project manager completes the Box Culvert Design Request Form.  Bridge culvert design must be complete by project turn in.  Preliminary bridge plans are typically not developed for culverts, unless they involve pedestrian underpasses. The box culvert design request form requires hydraulic modeling, box sizing, and foundations information to be complete and available.  Without this information, structural design cannot begin.

Bridge cost estimating

Bridge cost estimating occurs in all phases of the project development process. See bridge cost estimating fact sheet for more information.

Bridge projects initiated by local agencies on our Trunk Highway

Projects that are locally-initiated have followed a variety of routes for design, including the local agency retaining a consultant, MnDOT providing the design, or MnDOT retaining a consultant. With any initial discussions with local agencies regarding projects that will include a bridge on or over MnDOT right-of-way, we request the District or Area Engineer contact the State Bridge Planning and Hydraulics Engineer for early input on project delivery roles. The purpose of the discussion is to determine and have clear understanding of who will provide the bridge engineering and plan development. This should occur prior to the local agency taking action to retain a consultant.

If MnDOT staff is available to meet the project schedule, the MnDOT Bridge Office should perform the design and develop the plans for bridges that carry Trunk Highway traffic. Please contact the State Bridge Design Engineer as soon as possible to discuss staffing availability.  Similar consideration should be taken for bridges crossing trunk highways. For bridges that carry local roads, the Bridge Office will coordinate with the local agency's consultant. Local agencies who hire consultants for bridge design should contract with a firm on MnDOT's list of prequalified bridge consultants for the appropriate level of work.

A second purpose of early involvement with the Bridge Office is to coordinate with the local agency and their consultant on standards, adherence with MnDOT aesthetic themes on Trunk Highway corridors, and the cost participation policy. Early coordination with the Bridge Office will foster an understanding of all stakeholder expectations and expedite reviews and approval of plans for letting.

Similar coordination should also take place with the MnDOT Office of Materials and Road Research for foundation exploration, investigation, and reports.

Organizations involved