ABSTRACT
In the last two decades of the twentieth century, there was growing concern about pollution in major cities, and in particular about the large contribution made by road transportation sources to this problem (McNicol, Rand, and Williams 2001). Government legislation on internal combustion engine (ICE) emissions and fuel quality substantially improved the air quality in cities through a reduction of regulated pollutants. For example, in the United States, California introduced the so-called zero-emission vehicles (ZEV) mandate, which called for 2% of all new vehicles offered for sale in California in model years 1998-2000 to be ZEVs. Initially, it was intended that such vehicles would be battery-powered electric vehicles (EVs). Owing to the limitation of EV development, the regulations were relaxed to allow additional time for the technology to develop. During the development period, alternative-fuel vehicles were also considered. The advantages of hybrid electric vehicles (HEVs) are regeneration of braking energy, engine shutdown instead of idling, and engine driving under high-load conditions; these advantages are more noticeable in city driving. The key weakness of EVs, on the other hand, is that time is needed to recharge the batteries (Morita 2003). Bus systems possess features such as stable depots, routes, groups of commuters, times of operation and frequencies, so that research on finding alternative-fuel modes for public transportation is of high interest. Therefore, the purpose of this research is to evaluate the best alternative-fuel buses suitable for the urban area and to explore the potential direction of development in the future.
