A comparative evaluation of six transit bus engines (three diesel, one propane (LPG), one natural gas for vehicles (NGV), and one methanol) has been performed. The purpose of the program was to assess the exhaust emissions and fuel consumption of current state-of-the-art large alternative fuel engines.Engine dynamometer test work was performed at the Ontario Research Foundation (ORF) which allowed a detailed comparison of several alternative-fuelled engines versus their diesel counterparts. Test data includes steady-state brake-specific fuel consumption maps, torque and horsepower curves. Transient performance, fuel consumption and emissions information came from computer-controlled engine dynamometer runs of the Advanced Design Bus (ADB) test cycle as defined by US DOT/Booz. Allen & Hamilton (1)*.Engine speed and load requirements were determined from data supplied by Detroit Diesel Allison (DDA) for their 4 0 foot urban transit bus with Canadian DDA 6V71 NA (CSS) engine. This information was in the form of a computer printout which listed engine speed, load, transmission gear, vehicle acceleration and position as a function of time. These data were fitted to the ADB cycle requirements at the Ontario Ministry of Transportation (MOT) in support of this program. A listing of the engine speed and torque versus time for all phases of the ADB cycle was provided to ORF where it was implemented on a computer-controlled engine dynamometer.The results of the test program indicate that alternative fuels have a useful role to play in reducing transit bus engine exhaust emissions.