Public transportation
Introduction
The role of public transport varies widely in Asian cities. Although in some Asian cities public transport's mode share is very low (less than 5%), in most cities public transport vehicles -- usually buses, but also other indigenous modes -- carry the majority of public transport trips. These operate on fixed routes and are powered by diesel engines, which are a major PM emission source.
Policies for public transport to improve air quality can either clean the vehicles directly (e.g. engine upgrades, use of alternative fuels) or indirectly seek to influence modal shift (e.g. increase switching to public transport). Improvements to public transport proposed to reduce emissions or other service quality enhancements should be implemented in an environment where the operations are efficient and financially sustainable. Appropriate regulatory and contracting arrangements are therefore required to facilitate financial sustainability while ensuring that fares are affordable.
Physical measures such as bus lanes or segregated busways increase efficiency and thus contribute to financial sustainability.
But if public transport operators are not responsive to their patrons then much of the potential gain from these measures could be lost. Hence, measures to bring about efficiencies should also include some element of competition. Competition "for the market" backed up by appropriate regulation is usually be better for air quality than competition "in the market."
Many Asian cities have recently introduced new urban rail systems but in general to date they have failed to attract their forecast patronage (often less than 25% of forecast). Rail-based mass transport (the cleanest mode) has a role in the busiest corridors of our largest cities and could well be a later stage of a segregated busway system.
Appropriate integration of supporting feeder public transport services, facilities, ticking and public information systems are required. All too often integration is absent thus reducing the attractiveness of these rail and busway systems. This in turn reduces their ability to attract car drivers and in turn the potential reduction in emissions to the extent that freed space is not absorbed by new car trips previously suppressed because of congestion.
CNG and diesel buses compared
The California Air Resources Board (ARB) announces results from a study comparing emissions from diesel and CNG fuelled buses with emissions from a similar diesel bus equipped with advanced pollution controls.
"The data suggest that both CNG and diesel engines need additional emission controls, and with those controls both can achieve substantial and beneficial emission reductions," ARB chairman Alan Lloyd says.
The study tested two buses: one run on ultra low sulphur diesel and the other on CNG. Both buses were standard, 40-passenger vehicles equipped with Detroit Diesel Series 50 engines.
Two configurations were used, one with a Nelson's catalysed muffler, and the second with the muffler removed and replaced by a new Johnson Matthey CRT particulate filter (diesel/CRT).
Tests, from March to June of 2001, confirmed that both the CNG and diesel/CRT buses had lower emissions than the baseline diesel bus. The diesel/CRT bus produced lower mass emissions of particulate matter (PM) and toxic organic compounds than the CNG bus.
"When the diesel bus was refitted with a trap and run on low sulphur fuel its performance was very promising," Lloyd says.
However, both diesel buses produced higher nitrogen oxides (NOx) emissions, and the diesel/CRT bus exhibited a substantial increase in the nitrogen dioxide (NO2) proportion in the total NOx emission.
According to the ARB, additional control of NO2 and total NOx emission is required for filter equipped diesel buses. It was also concluded that additional control is required for the CNG bus emissions.
"We are working now to obtain better performance from CNG buses when they are equipped with state-of-the-art aftertreatment equipment," Lloyd says.
Tests are now being conducted by the ARB that will use the same CNG bus refitted with an original equipment manufacturer's oxidation catalyst and a new, state-of-the-art CNG bus equipped with a manufacturer installed oxidation catalyst.
Results of these tests should be available in mid-2002. The ARB also said it hopes to test a particle trap on a CNG fuelled bus, and will do so when a suitable trap becomes available.
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