In the last two decades of the 20th 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 et al.,
2001). Government legislation on ICE emissions and
fuel quality substantially improved the air quality in
cities through reduction in 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 EVs development, the regulations were
relaxed to allow additional time for the technology to
develop. During the development period