How MnDOT scores and selects bridge projects
MnDOT scores bridge condition needs when selecting projects to include in the Capital Highway Investment Plan. The selection of bridge projects is informed by district staff, experts from MnDOT’s bridge office and the Bridge Replacement and Improvement Management System (BRIM). MnDOT’s approach to managing bridges follows the guidance and targets in the Transportation Asset Management Plan and the planned outcomes in the 20-year Minnesota State Highway Investment Plan (MnSHIP).
MnDOT’s statewide performance measures for bridges are based on National Bridge Inventory (NBI) condition ratings, which measure the general condition of a bridge on a 1 to 9 scale. Ratings of 7 or higher are considered good condition, 5 and 6 are considered fair and satisfactory, and 4 or less considered poor.
Minnesota Statutes 165.14 Subd. 7 requires MnDOT to include a consideration of the risk of service interruption when prioritizing bridge repairs and replacements. MnDOT developed the Bridge Planning Index (BPI) to comply with the requirement for a risk-based prioritization system. BPI weighs the risks associated with the condition and fatigue of the bridge structure, potential damage from flooding and trucks, and impacts of detours.
Bridge that carry roads on the National Highway System (NHS) are scored and selected separately from bridge needs off the system. The allocation of funding between NHS and Non-NHS bridge needs is based on MnSHIP.
Once selected, MnDOT then identifies and evaluates alternatives and other needs, legal requirements, issues and opportunities in coordination with local partners, and considers public input. In the process, non-bridge work may be added to a bridge project or a bridge project may be combined with a nearby pavement project. The department follows a context-sensitive complete streets approach, which considers the needs of all users. The final project may address a substantial number of needs beyond the bridge need that precipitated the project. Projects may move years based on local coordination, project delivery, timing of other nearby construction projects, and funding shifts.
Project identification
Potential projects are developed and scored for all bridges: A) identified by BRIM and expert review for an action within the time period covered by the CHIP under development, and B) with deck, substructure or superstructure National Bridge Inventory (NBI) ratings based on the following table.
| Recommended Action from BRIM and Expert Review | Deck NBI Rating | Superstructure or Substructure NBI Rating |
|---|---|---|
| Overlay Deck | ≤ 7 | N/A |
| Replace Deck | ≤ 6 | ≤ 5 |
| Rehabilitation or Replacement | ≤ 6 | ≤ 5 |
Bridge rehabilitation includes superstructure replacement or widening and other activities as identified in Chapter 6 of the Bridge Preservation and Improvement Guidelines.
Scoring criteria and weights
NHS bridges are scored and prioritized statewide with input from district staff. Non-NHS bridges are scored statewide, but prioritized within each district.
Scoring multiple bridge structures
Projects involving significant work on twin bridge structures or other situations with more than one bridge, the score of the primary bridge driving the project will be the score for the overall project.
Bridge scoring
| Criteria | Points Available | Scoring Rubric for Re-decks, Rehabilitations and Replacements | Scoring Rubric for Overlays |
|---|---|---|---|
| Condition | 50 | NBI Deck, Superstructure, or Substructure Rating: ≤ 4 – 50 points =5 and/or fracture critical – 35 points |
NBI Deck Rating: ≤ 6 – 50 points =7 – 30 points |
| Risk of Service Interruption | 20 | Bridge Planning Index (BPI): ≤ 60 – 20 points 61-80 – 10 points >80 – 0 points | BPI: ≤ 60 – 20 points 61-80 – 10 points >80 – 0 points |
| Remaining Service Life | 20 | Deck RSL: ≤ 10 years – 20 points 11-15 years – 10 points >15 years – 0 points | Deck RSL: ≤ 20 years – 20 points 21-30 years – 10 points >30 years – 0 points |
| Bridge Size | 10 | Deck Area: ≥ 100,000 ft2 = 10 points 90,000-99,999 ft2 = 9 points 80,000-89,999 ft2 = 8 points 70,000-79,999 ft2 = 7 points 60,000-69,999 ft2 = 6 points 50,000-59,999 ft2 = 5 points <50,000 ft2 = 0 |
Deck Area: ≥100,000 ft2 and/or span length > 250 feet = 10 points 90,000-99,999 ft2 = 9 points 80,000-89,999 ft2 = 8 points 70,000-79,999 ft2 = 7 points 60,000-69,999 ft2 = 6 points 50,000-59,999 ft2 = 5 points <50,000 ft2 = 0 |
Scoring other types of bridge projects
Culvert needs
MnDOT replaces or rehabilitates most culverts (greater than 10 feet) in conjunction with other projects. However, MnDOT will occasionally select a culvert for a standalone project.
| Criteria | Points Available | Data Source / Basis |
|---|---|---|
| Structural Condition | 50 | NBI culvert rating: ≤ 4 – 50 points 5 – 35 points |
| Load Rating | 20 | Concrete Culvert: W Type in condition state 4 – 20 points W Type or condition state 4 – 10 points Corrugate Metal Culvert: Condition State 4 – 20 points Condition State 3 – 10 points |
| Channel and Waterway Condition | 15 | NBI channel condition and waterway adequacy ratings: ≤ 4 (channel) and/or ≤ 3 (waterway) – 15 points |
| Traffic Volume | 15 | Projects with AADTs equal to or greater than 10,000 in Greater MN and 25,000 in Metro receive full points. Below those values, points are assigned as a percent of those values rounded down to the nearest point. Example AADT of 14,000 in Metro: 14,000/25,000 X 15 points = 8.4 points rounded down to 8 points. |
Bridges carrying railroads over state highways
MnDOT uses the following to score and prioritize rehabilitation and replacement of bridges that carry railroads over state highways.
| Criteria | Points Available | Data Source / Basis |
|---|---|---|
| Condition | 70 | NBI deck, superstructure, and substructure condition ratings - specific ratings TBD |
| Vertical Clearance | 15 | <16 feet 4 inch clearance – 15 points (16 feet 6 inches on oversize/overweight super load corridors) |
| Traffic Volume | 15 | Based on AADT of road bridged. AADTs equal to or greater than 10,000 in Greater MN and 25,000 in Metro receive full points. Below those values, points are assigned as a percent of those values rounded down to the nearest point. Example AADT of 14,000 in Metro: 14,000/25,000 X 15 points = 8.4 points rounded down to 8 points. |
Pedestrian bridge and underpass rehab/replacement
MnDOT replaces or rehabilitates most pedestrian bridges and underpasses as part of other pavement and bridge projects. However, MnDOT uses the following to score and prioritize standalone projects.
| Criteria | Points Available | Scoring Rubric |
|---|---|---|
| Condition | 65 | NBI deck, substructure, superstructure or culvert rating: ≤ 4 – 65 points 5 – 30 of points |
| Proximity to key destinations | 15 | School, parks, senior residential facility, grocery store and/or other non-motorized traffic generator: w/in ¼ mile – 15 points w/in ½ mile – 10 points w/in 1 mile – 5 points Or part of a designated state or regional bikeway or trail – 15 points |
| ADA Compliance | 10 | Approaches and/or deck not ADA compliant – 10 points |
| Benefits Environmental Justice Population | 5 | More than 30% of the population in Metro and more than 20% of the population in Greater MN adjacent census tracts are covered by the Environmental Justice Executive Order |
| Low vertical clearance | 5 | < 17 feet – 5 points |
Factors not included in scoring
MnDOT considers a wide range of factors when selecting projects. These include considerations specific to individual projects as well as system level performance targets and guidance. Not all are included in the score.
Examples of reasons why a high-scoring project wouldn’t be picked
- Waiting to coordinate with another project
- Cost is greater than total available budget for year
- Waiting to avoid simultaneous or multiple years of detours in the same area
- Project not identified or prioritized in the metropolitan transportation plan or studies (for projects within MPO planning areas)
Examples of reasons why a lower scoring project would be picked
- Bridge is currently load posted
- To prepare for a future pavement or capacity expansion
- Ongoing maintenance concerns
- To coordinate with the timing of another MnDOT or local project