Some of us, though, actually enjoy driving.
On unleaded gas engines:
The Exhaust Gas Recycler systems on most modern cars DO make the net exhaust output at idle or any given RPM cleaner than it would be on the same system without them. The standards measure at the tailpipe. But, they do so at a performance cost - which means that the engine has to run harder to maintain adequate power - which burns more fuel to overcome the power lost to the EGR system.
This is in addition to vehicles having catalytic converters that finish burning the carbon monoxide into carbon dioxide. Although those do rob the engine of some power, they actually do their job fairly well.
On diesel engines:
Where VW got into trouble was on their diesel emissions - and that they had software designed to specifically alter the vehicle's emissions output during testing cycles. There are ways to make a diesel engine emissions compliant, but that usually involves complicated post combustion scrubbers to catch and process the soot. Those are expensive to install, maintain and require energy (power loss). VW avoided this simply by having their vehicles run in a lower power mode producing less exhaust during testing. Genius in a bad way. So, they got good on-road performance while spewing soot then would down-power while testing.
On emissions testing:
Current testing measures the ratio of pollutants per liter of exhaust gases coming out the tailpipe. So, manufacturers recycle emissions gases back through the engine and add air pumps into the exhaust system to increase the amounts of net gas coming out of the tailpipe which in turn decreases the pollution per liter of exhaust - even though it actually increases the pollution per operating mile.
Personally, I think it's time to change the whole emissions testing paradigm. Instead of net emissions per liter of exhaust gasses, I think it should be net emissions per unit of generated power at the wheels. This is easy enough to test/verify on a dyno hooked up to an exhaust chromatograph. This should be a measure of engine fuel to power combustion efficiency instead of a measure of devices engineered to, "pass the test".
Changing this mindset could make a modern engine design 15-20% more powerful. That translates into the same power with a lighter engine which translates to a lighter car which translates to less energy needed to accelerate which translates into greater distances traveled on less fuel while producing the same or less actual pollution.
The concept of using testing and goals for cleaner vehicles isn't a bad thing. The testing standards written into place by politicians with little to no concept of what actually defines 'pollution' and 'efficiency' are simply perpetuating a cycle of automotive engine designs made to fool the test.
