That's nice. CNG powered vehicles aren't allowed in most tunnels or even parking structures for safety reasons. Boston has a fleet of CNG busses. They're lovely, clean, and cheaper to run (or were when oil was higher), but they aren't allowed to run a whole bunch of routes that go through tunnels, underground busways, or have stops on the bottom deck of parking garages.
More green pinko policies that don't survive contact with reality.