High efficiency vehicle parking

We drive a 10 year old mini-van, one that my kids friends have a hard time opening the doors, since they are manual, not automatic.  We're not interested in replacing it, much to the disappointment of the kids, since we don't have the money for a new car right now.  Recently, my 8 year old noticed the painted spots in a parking lot, reserved for high efficiency cars.  She asked what that meant.  I explained that that car manufacturers can use new technology to make their cars use gas more efficiently.  If people purchase those types of cars, they can park in these reserved spots.  My 10 year old asked if our car was fuel efficient, I replied no, that technology wasn't around 10 years ago.  The 8 year old chimed in, saying 'well, we may not be using fuel efficiently, but we're certainly using money efficiently.'   I love her wit and wisdom.