White paper

Remote sensing of motor vehicle exhaust emissions

This report provides a comprehensive overview of vehicle remote sensing, an emissions measurement technique which has been used for more than 25 years to evaluate emissions from passing motor vehicles in real-world driving. We review technical details of the vehicle remote sensing test method, describe the multiple types of emissions analyses that can be conducted with remote sensing data, and explore areas where remote sensing can supplement emission test methods currently used in the European Union light-duty vehicle regulatory program.

Vehicle emission remote sensing differs from chassis dynamometer and PEMS testing in that the testing equipment does not physically interact with the vehicle undergoing testing. Rather, a light source and detector, placed either at the side of or above a roadway, are used to measure exhaust emissions remotely via spectroscopy as vehicles pass by the measurement location. In this way, remote sensing measurements yield snapshots of emission rates from thousands of individual vehicles as they are driven on actual roadways by their owners. Speed and acceleration are measured at the same time as the emissions measurement, providing information about the engine load. Finally, a camera captures an image of the vehicle’s number plate, allowing for the retrieval of essential vehicle information-make, model, model year, certified emission standard, fuel type, rated power-from vehicle registration databases. Thus, the ensemble of remote sensing measurements provides air pollutant emission rates for the fleet across a wide range of driving conditions.

There are many ways remote sensing data can be aggregated and analyzed to provide information on the emissions performance of in-use motor vehicles. Remote sensing data can determine emission rates for whole fleets, for specific vehicle types, for vehicle classes by emission standard, and even, given sufficient data are available, for distinct vehicle makes and models. Data can be used to evaluate the effect of parameters, such as engine load and ambient temperature, on vehicle emissions. Finally, remote sensing can be used to evaluate the durability of emissions control systems and to track the emissions performance of vehicle fleets over time.

To date, remote sensing has primarily been used in Europe for research applications. However, with the clear need for improved real-world control of vehicle emissions, there are a number of areas where remote sensing could supplement existing regulatory emission test methods. The very large sample sizes obtainable with remote sensing mean the method is well-suited for market surveillance and fleet screening applications. These data would provide valuable emissions information to authorities and would help in the identification of vehicle models with poor or suspicious real-world performance. This could then direct the more rigorous, and costly, measurement methods such as PEMS and chassis dynamometer testing as part of market surveillance programs. Similarly, the short- and long-term effectiveness of, for example, promised emission improvements can be tracked over time. Remote sensing can in addition be used to identify high-emitting vehicles, detect individual tampering, and encourage proper maintenance of vehicle emission control systems.

Figure ES-1