August 5, 2007
(Portland, OR) -- If you've caught a shuttle from a Portland International Airport parking lot to the terminal, you've experienced transit powered by compressed natural gas.
The airport's newest buses, 26 sleek silver models that carry their gas tanks on top, were built specifically to operate on CNG. They represent a significant investment in clean fuel by the Port of Portland: Each El Dorado bus cost $277,331, about $37,000 more than a diesel-powered model.
Natural gas - the same odorless, colorless vapor that heats houses across the Northwest - is one of many low-carbon vehicle fuels competing to get a toehold in the Northwest's fast-evolving green fuel market.
Led by California, West Coast states are trying both the carrot (tax incentives, guaranteed markets) and the stick (mandates that fuels contain a certain percentage of ethanol or biodiesel) to help jump-start the alternative-fuel market.
With a natural gas pipeline running through its property, the Port of Portland is ideally situated to tap the odorless, colorless gas, which is siphoned from the pipeline and stored in three cascading tanks at a pressure of 150 pounds per square inch.
When a bus arrives for refueling, the port's compressor ramps up the gas pressure to 4,000 pounds per square inch and then equalizes it at about 3,600 pounds before it is pumped by air nozzle into the tank. Invisible exhaust escapes through a small chimney on the roof.
Shuttle buses, with their short runs, are perfect for CNG, says Larry Madearis, head of maintenance for PDX. They can run all day on a tank of fuel, traveling an average of 200 miles, and be refueled at night.
The benefits are many: An overall 23 percent reduction in tailpipe emissions, no black diesel exhaust, a price break thanks to a federal rebate program. And putting the gas tanks on top of the bus leaves plenty of room for people and luggage.
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