not standard except with certain cargo vans.my guess it is probably something to do with exhaust entering into the van through some sort of physics due to the rear vortex.
wim commented on 11.20.10
sometimes it takes knowhow, we just smell them in our mind. looking at the car gives me a good feeling, the exhaustion pipe comes out at the side. It is indeed very safe, but is it customised or regular in the USA? Robert?