In recent years, in the wake of immense growth of society, humanities and industrial economy, the distances between cities and rural areas in Taiwan have been reduced considerably, and the demands for the transportation of passengers and freight have correspondingly increased. However, because the construction of mass rapid transit systems was not sufficient and lagged behind in schedule, diesel buses and trucks have become widely used, which are convenient and rapid transportation tools. Diesel engines, with their low cost of fuel and high horsepower output, have been widely used on passenger and freight vehicles and vehicles for special purposes such as those used in military and engineering functions. However, the black smoke (particle pollutants) emitted by diesel engines can cause discomfort to eyes. More seriously, such components as PAHs contained in the smoke may cause respiratory diseases and cancer. So it is seriously detrimental to human health.

The “Monthly Report on the Transportation Statistics of Taiwan” published by Ministry of Transportation and Communications shows the statistics of May 2004. They indicate that up to 14,694 freight vehicles were registered and up to 34,610 small trucks were registered, leading the other areas of Taiwan in both categories. Furthermore, the mass transportation in the Kaohsiung metropolitan area primarily depends on city buses. At the same time, there are large numbers of large diesel passenger cars. These vehicles have caused severe air pollution.

In recent ten or so years, in order to prevent exhaust emission by road transport from deteriorating air quality, advanced countries have worked hard to manage and reduce mobile sources of pollution, developed techniques for controlling pollution, and enacted relevant laws and regulations to improve environmental protection. The United States has accomplished the most in this aspect. In 1970 the United States established the system of regular examination and maintenance of gasoline- and diesel-powered vehicles in use and has since implemented it in various states. The system has given rise to excellent outcome, not only reducing the emission of vehicles by more than 90% but also benefiting the economic growth and international competitiveness of this country. So such countries as Switzerland (Europe) and Korea and Taiwan (Asia) have adopted the laws of emission control of the United States with the hope of reducing vehicle emission and improving the qualities of air. In reviewing the control system of the United States, it is known that the United States has increasingly tightened the standards for examining new vehicles and implemented the “System of Regular Examination and Maintenance of Vehicles in Use,” in consideration of the fact that most vehicles in use are old. This has played an important role in having improved the quality of air in urban areas and protecting national health.