Natural gas and hybrid fuel not suited to buses
We refer to the letter from Frank Gilbert ('Buses must be required by law to change fuel', September 17) regarding the feasibility of powering the Kowloon Motor Bus fleet by natural gas or hybrid diesel-electric.
As a socially responsible bus operator, KMB has continuously taken the initiative to provide a sustainable bus service by, for example, introducing ultra-low sulphur diesel and retrofitting all its older buses with catalytic converters in advance of government legislation. All newly purchased buses operate to stringent Euro III standards in line with the company's commitment to comply with or even exceed internationally recognised environmental standards.
KMB keeps in close contact with manufacturers and suppliers about the development of environmentally friendly measures, including fuel-saving and emission-reduction devices, as well as alternative fuels and power sources.
Regarding the application of natural gas in KMB's buses, a number of factors render this problematic at present. Safety concerns exist by virtue of the fuel's readiness to mix with air to form an explosive mixture. The consequences of such leakages would be especially serious in enclosed areas, such as tunnels and bus depots. This is a particular concern in Hong Kong with its uniquely high urban density and location of bus depots near residential areas.
In addition, the high global warming potential of the exhaust of natural gas engines has prompted many vehicle manufacturers to retard or even terminate research and development work on natural gas vehicles, with clear repercussions for operators in terms of required technical support. Another operational constraint to a double-decker bus operating on natural gas is that it would require a fuel tank four times the size of a diesel bus to cover the same range. This would greatly reduce the passenger-carrying capacity and have an adverse effect on transport efficiency.
Still, as a result of the technological advances made by KMB and the manufacturers, the emission performance of Euro III engines now is comparable to that of a natural gas engine.
Regarding diesel-electric hybrid, the technology for buses is still in its infancy, and is so far still limited to a small number of single-deck prototypes. Issues such as mechanical reliability, battery life, fuel economy, drivability and passenger capacity would need to be improved before diesel-electric could be seriously considered for a mass-transit bus fleet providing reliable services.