Trolley bus circuit breaker fires

In a July 7, 2020 letter, Los Angeles World Airports (LAWA) informed the National Highway Traffic Safety Administration (NHTSA) of three separate fire incidents resulting in the total loss of eight of its Spirit of America trolley buses. These buses were manufactured by ARBOC Specialty Vehicles, LLC (Arboc) on incomplete chassis from Freightliner Custom Chassis Corporation. Considering the safety concerns and substantial losses, LAWA grounded the remaining buses in its fleet. On January 15, 2021, NHTSA opened an investigation to determine if a defect in the subject vehicles exists and presents an unreasonable risk to vehicle occupants and nearby people or property. On February 24, 2021, the Office of Defects Investigation (ODI) sent an Information Request (IR) letter to Arboc. On April 8, 2021, ODI received an IR response from Arboc that included information on vehicle production, consumer complaints, field reports, warranty claims, manufacturer actions, vehicle changes and other data related to the alleged defect. On June 29, 2021, Arboc sent NHTSA a copy of an investigation report/update (Investigations into LAWA Thermal Events) done by a third-party investigation firm (hired by the chassis manufacturer) that included an assessment of the alleged defect/fires. ODI also engaged in discussions with the manufacturer about the alleged defect on multiple occasions during this investigation. Upon analysis of available data, ODI has not determined the existence of a safety defect. The third-party investigation report points to the 30-amp recessed circuit breaker as the hottest point in the vehicle during the December 21, 2019 fire (first fire) and suggests that it could have been a root cause for that fire. However, that report is inconclusive. Based on available information, the causation of the two subsequent fires appears unrelated to the circuit breaker. The second fire (February 2020) appears to have been caused by technician error during repair of fleet vehicles by