The state Department of Transportation says its fleet of 11 electric buses remains out of service following a battery fire in July that triggered a federal investigation. The National Transportation Safety Board issued a preliminary report about the fire in September detailing how the 40-foot long electric bus operated by CTtransit became engulfed in flames while parked at a maintenance facility. The incident sent two maintenance workers to an area hospital where they were treated for smoke inhalation. “The battery electric buses remain out of service while the investigations are ongoing,” DOT spokesperson Josh Morgan said in an email. Both the NTSB and the Connecticut State Police are investigating the fire’s origin and its cause.