In early 2021, MxV Rail began testing three intermediate strength (IS) rail types along with a standard strength (SS) rail type on a 5-degree curve at the Facility for Accelerated Service Testing (FAST®) in Pueblo, CO. After the rails were installed in January 2021, 141 million gross tons (MGT) of traffic were accumulated through June 2021, and the results were published in a previous Technology Digest.! The rails have since continued to accumulate more tonnage, and this Technology Digest summarizes the findings of testing performed from 141 MGT through 336 MGT. At 282 MGT, the rails were moved from their original installation location on a track known as the High Tonnage Loop (HTL) to a similar 5-degree curve in MxV Rail’s newly constructed FAST loop. Testing resumed in November 2023 and rails have continued to accumulate tonnage at the new site. The 5-degree curves in both the HTL and the…