NYC tried to require that taxi cabs be hybrid-vehicles but courts have struck-down the regulation. That's both good news and bad news. It's good news because hybrids were not the correct direction to go. It's bad news because something does need to be done about city air pollution.
Now instead of hybrids I suggested the Mercedes Benz E-Class Bluetec turbo-diesel. Of course I wasn't requiring the luxury of the MB E- Class just the engine technology and the sedan size. Well, the turbo- diesel has the perfect torque characteristic for city driving and the fuel mileage is very good. But this is the wrong direction also.
The correct direction is to legislate five years into the future and say that in the year 2016 all taxi cabs must be either chargeable electric-vehicles or hydrogen fuel-cell electric vehicles. Why ? Well, Tesla is on the verge of building an electric-vehicle sedan that can go up to 300 miles on a charge and that with the third optional battery pack. And then charging at a commercial charge station can be done in as few as 45 minutes. But both MB and Honda say that they can mass-produce fuel-cell electric-vehicles beginning in the years 2013 to 2015. And the advantage of the fuel-cell vehicle over the chargable electric-vehicle is greater range. Furthermore any metro that has a few fuel-cell buses running do then have a hydrogen fueling station.
Now in that way the taxi cab industry would decide the better of the two technologies and the car industry would decide what to offer.
But if the major cities can't legislate taxi cab specifications they can run fuel-cell buses since the cities are the bus fleet operators. And here fuel-cell buses do currently exist and are in the process of being proven.