along with the lab-based procedure, the unece introduced a test in real driving conditions for nox and other particulate emissions, which are a major cause of air pollution. this procedure is called real drive emissions test (rde) and verifies that legislative caps for pollutants are not exceeded under real use. rde does not substitute the laboratory test (the only one that holds a legal value), but they complement it. during rde the vehicle is being tested under various driving and external conditions, that include different heights, temperatures, extra payload, uphill and downhill driving, slow roads, fast roads, etc.