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New York City plans to convert hybrid buses to diesel

3 July 2013

The New York City public transit agency, MTA, plans to retrofit 389 hybrid buses—23% of its entire hybrid fleet—with diesel engines and convert them to all-diesel configuration, according to a report by the New York Post.

1,677 out of 5,719 city buses in New York City are hybrids. A five-year warranty is set to expire on a number of buses, meaning that the MTA would now have to carry the cost of repairs. MTA insiders were quoted to say that the hybrids must be constantly repaired by maintenance workers. The electric traction motor—an expensive component of the hybrid powertrain—has been reportedly experiencing particularly high failure rates.

Hybrid buses operating in Manhattan will not be phased out because they stop more frequently, and the electric components of hybrid powertrains apparently function better with more stops. Due to the regenerative braking, fuel efficiency of the hybrids also becomes better in stop-and-go traffic.

Following a trial with five hybrid buses in 1998, the MTA began phasing out conventional diesel buses in favor of diesel-electric hybrids. The first 10 hybrids cost $1 million each. When the agency last ordered hybrids, it paid $700,000-$800,000 per bus.

MTA has not purchased a hybrid in three years—since 2010 the agency has been purchasing all-diesel buses due to their better fuel efficiency compared to hybrids. The cost of a diesel bus is on the order of $500,000.

Back in the mid-2000s, the hybrids could offer not only a fuel economy advantage but also lower emissions—the hybrids ordered by New York City were equipped with diesel particulate filters ahead of regulatory deadlines. However, 2010 and later diesel engines have both better fuel economy and very low PM and NOx emissions compared to older diesels.

Fuel consumption in hybrid buses is very sensitive to the test cycle, as it depends heavily on regenerative braking (the recovery of the bus braking energy in the form of electricity). Transit agencies in a number of cities became disillusioned with the real life fuel efficiency of hybrids—especially so when the buses were operated on suburban routes with fewer stops. Transit operators in colder climates, including the cities of Toronto and Ottawa in Canada, also complained about the high cost of battery replacements in hybrid buses.

Source: New York Post