The buses on the routes around here in Dundee are electric hybrids with flywheels to recover braking energy which with the hills here can be significant. We live at the top of a 60m hill and the double deckers sitting at the lights at the bottom of the hill can turn the corner onto the main road and get up the shallow incline to the bus stop entirely on the flywheel. You can hear it. The bus company, a division of First Bus, says they are performing very well and saving significantly on fuel costs. They are also much lower in emissions. There's a narrow winding canyon like road in the town a lot of buses use (right by the central bus station) that can have very high PM10 etc levels with idling bus diesels, especially in the winter. So these buses decrease that output significantly.