Increasing environmental concerns and unstable fuel prices have made hybrid vehicles (HEVs) and battery electric vehicles
(BEVs) more and more interesting as viable replacements to conventional vehicles. These types of vehicles have already
been available on the passenger car and heavy vehicle markets for more than ten years. Therefore, viability of the related
powertrain technology has already been proven and acceptance by customers has been attained. Despite of the technological
success, life cycle costs of the HEVs and BEVs are still, in most cases, higher than the costs of the conventional vehicles
hybrid and electric city buses for fleet operation.