On October 12, 2021, about 4:49 p.m. local time, Washington Metropolitan Area Transit Authority (WMATA) train 407, consisting of 8 railcars and carrying 187 passengers and the operator, derailed while traveling from Rosslyn Station toward Arlington Cemetery Station on the Blue Line in Arlington, Virginia. The derailment occurred in a tunnel south of the Rosslyn Station platform. All railcars remained upright and in-line. The passengers and operator were evacuated to Arlington Cemetery Station. No injuries were reported; one passenger was transported to the hospital, treated, and released.
The derailment occurred because the wheels of one wheelset had migrated outward on their axle, resulting in a width larger than the design specification. The wheel migration happened over time, eventually causing the wheelset to exceed its maximum design width. When this wheelset traveled over a turnout (a type of special track work that allows a train to change tracks), the out-of-specification wheelset width caused a wheel to leave the rail, derailing a railcar.
We found that one department within WMATA was aware of wheel migration in its railcar fleet and attempted to mitigate the associated safety risks, but the department did not conduct a trend analysis to monitor the incidence of wheel migration or how effective its mitigations were. A trend analysis would have shown the increasing incidence of wheel migration and made an effective response more likely. WMATA has since made improvements to its safety management systems and has plans to expand its use of trend analysis and related tools to identify and mitigate safety risks before accidents occur. The oversight of the Washington Metrorail Safety Commission is vital to supporting and monitoring these ongoing improvements.
We determined that the probable cause of the derailment of Washington Metropolitan Area Transit Authority train 407 south of Rosslyn Station was an out-of-specification wheelset that caused a wheel to depart the rail at a turnout; the wheelset was out of specification because the wheelset’s design allowed the wheels to migrate outward and eventually exceed the maximum permitted back-to-back measurement.
We recommended that WMATA implement processes and resources to expand its use of trend analysis to identify and mitigate safety risks. We also recommended that the Washington Metrorail Safety Commission develop a program to support and monitor WMATA’s expanded use of trend analysis, both to ensure that it remains compliant with federal guidelines and to assess its effect on safety.
