first tested by SunLine Transit Agency. During revenue service with SunLine, the HHICE engine overheated twice and caught fire once in three separate incidents in 2007. Transport for London ordered ten hydrogen-powered buses from ISE in 2007, split equally as five fuel cell and five HHICE APU buses. Clients Selected users of transit buses equipped with ISE hybrid drivetrains included: References External links Defunct companies based in California