The Performance of Diesel Taxicabs in New York City Taxicab Fleets

Abstract

A test group of 66 diesel-powered taxicabs, paired with an equal number of gasoline-powered cabs, were operated in three taxicab fleets in New York City to determine comparative differences in fuel economy, exhaust emissions, reliability, and maintenance requirements. The cabs were identical, except for their engines, which were either Nissan 198 CID diesel engines or Chrysler 225 CID gasoline engines. The test disclosed that the diesel-powered cabs averaged 14.7 mpg fuel consumption while gasoline-powered cabs averaged just 9.7 mpg. The fuel consumption superiority of the diesel-powered cabs was to be expected as the diesel engine is more efficient than the gasoline engine under conditions of low piston speed, i.e. the low driving speed (7 mph) of taxicabs in the traffic-congested urban environment. The margin of superiority, however, was not as great as expected, possibly due to different driver behavior. Exhaust emissions tests were made on both groups of taxicabs after 5000 and 50,000 miles of driving. At both mileage levels, diesel engine emissions were substantially lower than gasoline engine emissions in carbon monoxide, hydrocarbons, and nitrogen oxides. The degradation of the diesel exhaust emissions with time was also much less than that of the gasoline emissions. Preliminary analysis of vehicle maintenance through analysis of mechanic labor hours, shifts lost, and miles driven on a shift revealed that diesel cabs required slightly less maintenance than gasoline cabs. It is surmised, however, that the maintenance/reliability records of diesel cabs were somewhat downgraded due to problems resulting from engine retrofitting and delays due to mechanics' unfamiliarity with diesel engines (consequent inclination to service gasoline cabs first), and difficulties in obtaining spare parts for the diesel engines.