An emission test cycle, also known as a smog check, is a specifie procedure for measuring pollutant emissions of engines. For emission measurements to be comparable for different engines in a category, the measurements are performed under a specific operating pattern, or 'test cycle' of alternating high, medium, and low engine load. The test cycle should ideally reflect a 'normal' usage pattern concerning speed and acceleration. Realistic test cycles are instrumental for the environmental integrity of emission standards. It was recently discovered that engine manufacturers would engage in 'cycle beating' to optimize emission performance to the test cycle against which European vehicle emission standards were tested, with the result that real-life emissions would be much higher than expected, undermining the standards and public health.