One of the most aggressive ‘clean fleet’ programs in the country.” That's how John Walsh, chief maintenance officer, bus department, New York City Transit Authority, describes the NYCTA's current efforts, which, he said, are “technology neutral” and involve some 4,500 buses.
Compressed natural gas (CNG) buses have become the “gold standard” for clean transit, Walsh told attendees at the recent SAE Truck & Bus Meeting in Portland, Ore., but he noted that their emissions benefits continue to come at an extremely high price. In addition to costly infrastructure requirements, NYCTA's CNG buses cost 20¢ more per mile for maintenance and 16¢ more per mile for fuel than the diesel buses.
And diesel engine makers have done an amazing job, he added. “Current engines, especially those for buses, are 94% cleaner than those sold ten years ago.”
Hybridization of the diesel drivetrain in buses reduces all four emissions criteria (CO, HC, NOx, PM) dramatically, and in some cases makes the emissions profile look like that of a CNG bus, Walsh said. NYCTA has operated diesel/electric hybrid buses since September 1998. To date, its 10 hybrids have logged 200,000 revenue miles and “have performed better than expected.” Another 125 are on order, and a tender is being prepared for 175 more for delivery in 2003.
NYCTA bus plans outlined by Walsh include:
390 hybrid buses by 2005
Retrofitting all diesels (about 3,500 buses) with catalyzed exhaust filters by end of 2003.
All buses will continue to use low sulfur fuel.
Retiring all pre-1993 two-stroke diesels by 2003, replacing them with EGR-equipped diesels.