What is the purpose of load rating in NBIS, and what are LRFR and LRFD?

• A. To rate bridges only for construction permit purposes; LRFR and LRFD are unrelated.
• B. To determine if a bridge can safely carry traffic loads; LRFR is Load Rating for Routine (existing loads); LRFD is Load and Resistance Factor Design-based rating for capacity.
• C. To estimate construction costs; LRFR and LRFD are financing metrics.
• D. To determine maximum speed limits; LRFR/LRFD refer to fatigue.

Answer: (B)

Load rating in NBIS is about assessing whether an existing bridge can safely carry the traffic loads it experiences and whether restrictions are needed to protect safety. It’s a safety check on current capacity, not about how a bridge is designed or financed, or about construction permits or speed limits.

LRFR, Load Rating for Routine, uses standard live-load models that represent typical traffic and applies the bridge’s current condition to determine a rating of its ability to carry those loads. It tells you if a bridge can safely support routine, everyday traffic on an existing structure.

LRFD, Load and Resistance Factor Design-based rating, uses the design-strength framework with load and resistance factors. This rating reflects the capacity as determined under modern design principles, often used to compare against design-based expectations or to rate capacity with a consistent safety philosophy.

So the best answer is that the purpose is to determine if a bridge can safely carry traffic loads, with LRFR describing routine-load ratings for existing bridges and LRFD describing a design-based rating approach.