Missouri Bridge Rating by LRFR and LFR Methodology – A brief summary

Feb 11, 2023 | Engineering | 0 comments

I am currently working on a research project at the University of Missouri-Kansas City (UMKC) under the guidance of my professor, Dr. Ganesh Thiagarajan and senior colleagues, Bao Tran, and Ronald Cheruiyot. In this project, each of us is working on different types of bridge, Bao on Prestressed Bridges, Ronald on Steel Bridges, and myself on Concrete Bridges. There were several more members before I joined halfway through to the project. Today in this blog, I am going to describe what I did during the project.



The Missouri Department of Transportation (MoDOT) currently uses the Load Factor Rating (LFR) methodology to load rate highway bridges across the state. However, the American Association of State Highway and Transportation Officials (AASHTO) has come up with supposedly better methodology the Load and Resistance Factor Rating (LRFR) methodology. So, this research is conducted to compare the LFR and LRFR methodologies and determine which method is more effective in load rating bridges.


Load rating is a process of determining the live load capacity of a bridge. A rating is expressed as a numerical value, in which a rating of 1.0 or higher means the bridge can safely carry the vehicle it was rated for. Each structural component is rated individually, with the lowest rating controlling the overall rating of the bridge.
There are two different levels of load rating, Inventory and Operating.

  • The inventory rating represents the routine live load capacity that a bridge can support over an indefinite period of time.
  • The operating level rates the bridge for the live load capacity for less frequent vehicles.

Technical Terms:

Rating Load – The maximum load that a bridge can safely carry. It is determined by a load rating analysis, which takes into account the bridge’s design, condition, and the type of vehicles that are expected to cross it.

Rating Factor – A number that is used to express the rating load as a percentage of the bridge’s design load. For example, a rating factor of 1.25 means that the bridge can safely carry 125% of its design load.

Posting Load – The maximum load that is allowed to cross a bridge. It is typically lower than the rating load, to account for the possibility of unexpected loads or damage to the bridge.

Types of Missouri Department of Transportation (MoDOT) vehicles

  • State Legal vehicles
    a) H20L – Single Unit Truck
    b) MO3S2 – Combination Truck
  • Commercial Vehicles
    a) CZSU – Single Unit Truck
    b) CZRT – Combination Truck

Types of American Association of State Highway and Transportation Officials (AASHTO)Vehicles

  • AASHTO Legal load
    a) Type 3
    b) Type 3-3
    c) Type 3S2
  • Special Hauling Vehicles
    a) SU4
    b) SU5
    c) SU6
    d) SU7


This study used a representative sample of 99 Concrete bridges across Missouri state. The bridges were rated using both the LFR and LRFR methodologies using “AASHTOWare Bridge Rating” software. The results of the ratings were then exported as the excel file and used for analysis.

The Analysis included the detail comparative study of LRFR and LFR Methodology of MoDOT vehicles and AASHTO vehicles (Single Unit Vehicle vs Single Unit Vehicle, Multiple vs Multiple). Then, the points were plotted to get the graph and the Threshold Load, Factor, Posting Load, and No. of bridges to be posted were determined.

Some of the Graphs obtained during the Analysis.


The results of the study showed that the LRFR methodology was more effective in load rating bridges than the LFR methodology. The LRFR methodology resulted in higher ratings for the majority of the bridges in the study. This suggests that the LRFR methodology is a more accurate way to determine the live load capacity of bridges.


The results of this study suggest that the LRFR methodology is the preferred method for load rating bridges. The LRFR methodology is more accurate and results in higher ratings for bridges. This means that bridges rated using the LRFR methodology are more likely to be able to safely carry the vehicles they were designed for.


Do leave your thoughts 😉