Growing concern about energy conservation and exhaust gas emissions from heavy duty engines of trucks and buses has increased the demand for the use of alternate fuels. A unique transportable testing laboratory designed to measure specific constituents of exhaust gas emissions from the engines of heavy duty vehicles operating on conventional or alternate fuels has been constructed by a team from West Virginia University. In this transportable facility, a special flat-bed trailer has been constructed to accommodate drive train units, free-rotating rollers, power-absorbing units to simulate road load, and flywheels to simulate vehicle inertia. Four hydraulic jacks are used to lower it to the ground at the fleet site. This allows the tested vehicle to be driven onto rollers embedded in the flat-bed. Hub adapters are connected at the outboard wheel locations at each side of the drive shaft of the vehicle. A companion trailer has been constructed to accommodate the exhaust gas analysis system which includes both full and auxiliary exhaust flow dilution tunnels, and exhaust gas analyzers for CO, CO2, NOx, and HC. Particulate emissions, methane, formaldehyde and methanol are also measured. The instrument trailer also contains a computer-based data acquisition and control system, and other necessary accessories to monitor such parameters as torque, speed, flow rate, and temperature.