Rigging cars to pass emissions tests has been a game for a long time. For a long time all you had to do was pass a tailpipe sniff test on a dyno and the car wo

Rigging cars to pass emissions tests has been a game for a long time. For a long time all you had to do was pass a tailpipe sniff test on a dyno and the car would be held at two slow speeds for the duration of the test, so you'd get results for those kinds of cruising situations but not for acceleration or highway operation. So, cars were adapted to pass these tests. Later when fuel economy rules came about, the same thing happened: the test cycles for fuel economy were examined and cars were changed to achieve better results just for these tests.