Parry People Movers ( PPM ) is a British company manufacturing lightweight railbuses that use Flywheel energy storage ( FES ) to store energy for traction . Parry People Movers Ltd. ( PPM ) is a British company manufacturing lightweight trams and railcars that use flywheel energy storage ( FES ) to store energy for traction , allowing electric systems to operate without overhead wires or third rails , and railcars fuelled by small gas , diesel or hydrogen engines , offering very high energy efficiency and very low emissions , suitable for new-build or existing rail systems in a variety of gauges , serving both urban and rural communities in any part of the world .