The paper describes Shell's mobile instrumented vehicle for measuring road performance and exhaust emissions. Information is given on the design criteria and construction features of the vehicle and its instrumentation system. Test results show typical applications of the vehicle in providing data on the effect of engine adjustment and component condition on performance, fuel economy, and exhaust emissions.Instrumentation in the vehicle includes exhaust-gas analyzers to measure unburned hydrocarbons, carbon monoxide, nitric oxide, and carbon dioxide concentrations in the exhaust gases. The center of the system is a 40-channel magnetic tape data logger which can accumulate approximately 1.5 million data points per hour. The data logging system includes 10 operating parameters, 10 exhaust gas temperatures, and 20 vehicle and engine temperatures. Accumulators are used to log time, distance, and fuel consumption. Manual data are also logged as an event reference. The data acquisition system allows an efficient manipulation of the data using high-speed computer facilities.The concept of the system is to provide sufficient instrumentation flexibility to permit measurements of emission and road performance parameters under realistic road conditions.