By Barbara Kessler
Green Right Now

You’ve heard the saying, “it’s easy being green.” Maybe sometimes. But not always, and not if you’re the Dallas Area Rapid Transit (DART) agency, which finds itself tangling with a green dilemma.

DART, which serves Dallas and 11 other cities in the region, has been planning to replace its aging bus fleet with 537 shiny new buses. It’s a great opportunity to go green with the entire fleet.

But after taking bids this fall and updating the research, the agency members are locked in debate over what type of buses are “cleaner” and which ones make the most sense environmentally and economically. The answer is not readily apparent. Like potential car buyers on the threshold of a dealership showroom, the bus-buying members of DART find themselves puzzling over the new technologies and old perceptions.

They are comparing diesel buses against those that run on compressed natural gas (CNG) and also considering the newest buses on the block, diesel-electric hybrids.

The hybrids are clean machines, with the fewest greenhouse gas emissions. They’re also the smoothest riding — and by far the most expensive. The CNG buses, meanwhile, have a reputation for cleaner emissions than traditional diesel buses. But compared to newer diesels, those emissions differences may have gone up in smoke.