Following the chief executive s policy address in 1999 on environmental improvements and his stress on the priority in improving air quality in the policy address in 2000 , transport department continues to take active measures to ameliorate air quality . these measures include replacing diesel taxis with liquefied petroleum gas ( lpg ) taxis , exploring the use of electric light buses , controlling the growth of the franchised bus fleet , enhancing bus operations in congested areas , introducing bus - bus and bus - rail interchange schemes , improving vehicle emission , and implementing pedestrian schemes 随著行政长官在1999年施政报告中提及改善环境及在2000年施政报告中再次强调优先改善空气质素后,运输署继续积极采取适当措施改善空气质素,包括将柴油的士转为石油气的士,研究使用另类燃料的公共小巴,控制专营巴士车队的增长,改善在交通挤塞地区的巴士运作情况,推广巴士转乘计划,和实施行人环境改善计划。