MxV Rail has installed a new steel bridge span at the Facility for Accelerated Service Testing (FAST®) in Pueblo, CO. Designed and donated by the National Steel Bridge Alliance (NSBA), this span includes several important differences from both typical railroad bridge design and American Railway Engineering and Maintenance-of-Way Association (AREMA) recommended practices. At the request of the Association of American Railroads (AAR) Bridge Technology Advisory Group (Bridge TAG), the span is being evaluated in a heavy haul environment for both overall performance and specific design details as part of the AAR’s Strategic Research Initiatives program. BACKGROUND Steel has been used for railroad bridges for over 150 years. Longer spans require built up girders or trusses, but shorter spans often use rolled steel beams as the primary members. Early beam span bridges typically used rolled beams riveted together under an open deck or a separate ballast deck. Advances in steel rolling,…