Are CNG buses really beneficial?

With diesel buses emitting more nitrogen oxide in our atmosphere, many public transportation agencies switched to CNG buses. CNG buses produce less noise levels, engine vibration, and emit less nitrogen oxide than a modern diesel bus. However, diesel buses are cleaner in carbon monoxide and hydrocarbons (both a factor in ozone). CNG buses brake down more than twice as often: On an annual basis CNG averaged about 32,000 miles while diesel buses annual average was 51,000 miles.* The maintenance cost of a CNG bus fleet can become very costly in the long run. Also CNG buses are heavier than diesel buses due to the weight of the heavy-duty CNG tank and thus raising the cost of street repair. Are CNG buses really worth the long term headache? With DART getting ready for their new fleet of CNG buses; I am looking forward to their long term results.

*(SOURCE: Memorandum "CNG and Diesel Comparative Analysis" BY Elaine Timbs, CMTA Chief of Maintenance, dated September or October of 1997)