(Source: Federal Railroad Administration press release, June 23, 2016)
WASHINGTON, D.C. — Conclusion: Unless or until additional details come to light, FRA has made the preliminary determination that Union Pacific’s failure to maintain its track and track equipment resulted in the derailment. Broken and sheared lag bolts, while difficult to detect by high-rail, are more detectable by walking inspection combined with indications of movement in the rail or track structure and/or uneven rail wear, and are critically important to resolve quickly.
FRA’s preliminary investigation determined the Union Pacific derailment was caused by broken lag bolts leading to wide track gauge. FRA’s investigation found that multiple lag bolts in this section of Union Pacific track were broken and sheared, leading to tie plates loosening from ties. The loosened tie plates allowed for the rails to be pushed outwards as trains moved across them, eventually resulting in an area of wide gauge, leading to the derailment.
Full story: www.fra.dot.gov