Environmentally aware San Antonians are getting the last laugh under a new program allowing drivers of hybrid vehicles to park for free at city meters, while the drivers of Hummers, SUVs and trucks still have to dig around for change. Park your hybrid at a one-hour meter? Save a buck. Stop at an all-day meter? That's $2 left in your coin purse. The city's pilot program, which has enrolled about 150 hybrid drivers since it started in May, is part of the growing national trend toward rewarding the environmentally conscious.