DILLON — The Montana Department of Transportation (MDT) recently issued new load postings for the Grasshopper Creek Bridge [bit.ly] twenty-one miles west of Dillon in Beaverhead County. The postings are part of a multi-year effort to update load ratings and postings on Montana bridges as mandated by the Federal Highway Administration [highways.dot.gov] (FHWA).
The FHWA mandate is in response to changes in the trucking industry over the last decade. Truck manufacturers are building specialized hauling vehicles (SHVs), which are capable of legally carrying heavier loads than typical vehicles have in the past. SHVs are single-unit, short-wheelbase, multiple-axle trucks commonly used in the construction, waste management, bulk cargo and commodities hauling industries. Often times one or more axles can be raised or lowered as needed to comply with statutory weight limitations.
These SHV configurations concentrate heavy loads over a short length, and they have been found to overstress bridges beyond what was previously modeled by standard commercial vehicles. To account for their increasing presence and ensure safe operation, FHWA has determined that all states must include these new, short, heavy vehicles when evaluating the safe limits of bridge capacity.
To comply with the mandate, MDT is currently updating load ratings for 4,500 public bridges across the state, including approximately 2,500 owned and maintained by MDT. This effort is expected to take about four years to complete.
Bridge weight restrictions are required when the engineering analysis of a bridge, known as a load rating, indicates that it cannot carry standard, legal loads. Load ratings provide information about how much distributed weight can safely pass over a bridge. Load posting signs show maximum weight limits for different vehicle types, depending on their axle configuration. A posted bridge is safe to use, but the weight of certain vehicles must be limited accordingly.
The new posting on the Grasshopper Creek Bridge applies to SHVs; it limits the maximum gross vehicle weight of single-unit vehicles with 4, 5, or 6 axles to 17 tons and 7 axles to 21 tons.
Further information on understanding and interpreting Montana’s weight limit signs and silhouettes can be found in MDT’s load posting brochure, located here: [bit.ly]http://bit.ly/mtbridgebrochure [bit.ly].
The exact location of the Grasshopper Creek Bridge is viewable on Google Maps here: http://bit.ly/GrasshopperCreek [bit.ly].
To assist with public outreach and education about the bridge load posting program, MDT has created an interactive map with statewide load posted bridge locations available here: [bit.ly]http://bit.ly/mtbridgemap [bit.ly].
For questions about the program or specific bridges, please call the project hotline at 1-888-824-8445 or email MDTbridgeloadposting@mt.gov.