Diesel burns cleaner than gas, bur compressed natural gas (CNG) burns cleaner than diesel. That's why TriMet is considering the purchase of buses that burn CNG.

“TriMet has been exploring numerous green transit options and is currently analyzing the costs and benefits of adding CNG buses to the fleet,” said TriMet General Manager Neil McFarlane. “The option to buy CNG buses is part of TriMet’s ongoing effort to increase our sustainability and improve air quality throughout the region.”

The transit agency needs to determine whether change is the right thing to do financially. The CNG buses cost $55,000 more than a diesel bus that costs $420,000.  They are also not as efficient as diesel and they get lower mileage.  Maintenance is also higher.

Offsetting the negatives is the more stable and reduced cost of CNG. TriMet wants to runs tests to determine whether it's worth the change.  Several other transit agencies use CNG and they'll look at that history and how it's worked in those applications.

It's not just a matter of buying new buses, but TriMet would also have to modify a maintenance facility to repair the buses.  The Merlo garage in Beaverton is under consideration.  CNG must be stored in high pressure tanks, so a new fueling system would have to be added.

The buses would be purchased with federal and state grants and under the current bond program being used to buy new buses.

If TriMet decides to move forward, buses would start being purchased in 2015.