As hybrids become more popular among consumers, they're also trickling into the taxicab fleets of America's larger cities. Ford reports that 31 Escape SUV hybrid taxis have already traveled a combined 100,000 miles in San Francisco. Chicago is adding hybrid cabs, too, and 18 hybrid taxis just went into service in New York City. The eco-friendly cabs are also making the rounds at auto shows, including April's New York International Auto Show.

Hybrids and alternative-fuel vehicles are ideally suited for taxicab and town car fleets. Most cabs drive at city speeds in stop-and-go traffic. This creates opportunities for regenerative braking, in which the resistance of electric generators slows the car and recharges the nickel-hydride batteries.

Cabs can also use clean-burning compressed natural gas (CNG) or propane. Even with the more limited range of natural-gas vehicles, a driver's shift usually ends before the tank runs dry, and since drivers go back to the taxi barn between shifts, the limited availability of CNG refueling stations elsewhere is not much of an issue. In Europe, diesel vehicles are popular as cabs (also as passenger cars and trucks), because diesels idle on a fraction of the fuel of a gas-engine car.

San Francisco cabbies generally give high marks to hybrid vehicles. Fuel costs are lower with hybrids, a benefit for the drivers who pay for their own fuel. Cabbies say that customers appreciate the extra space in the SUV Escape, and in the green-centric City by the Bay, some passengers tip better because they're riding in hybrid vehicles. And the hybrids' brakes last longer because of regenerative braking.

Part of the dollars-and-cents economics of hybrid cabs may come into focus shortly, though: specifically, the rated lifespan for the hybrid batteries that constitute a big chunk of the Escape hybrid's $4,000 premium. The fuel savings accrue to the drivers, but the cost of replacing the batteries once they're out of warranty is on the shoulders of the fleet owners.