I believe in NYC you either had to use the official NYC cab, formerly a stretched Crown Vic, soon to be a Nissan SUV, or you had the option in recent years of using an approved hybrid. Guess which is not just much cheaper to buy, but also much cheaper to operate? San Francisco has been requiring that all cabs be hybrids for a few years. I bet Boston has a law, too. In practice a hybrid is perfect for cab use. Excellent city gas mileage, and the engine and brakes are less stressed than non-hybrids.
When the NYC fleets started experimenting with them a few years ago they were amazed at how long the brakes lasted. They also found the hybrid drivers were getting in fewer accidents. My guess is the old Crown Vics made the drivers feel more protected, and they were more likely to cut off other drivers and engage in other hazardous behavior. I hate the cabbies there, but I like them in San Francisco. It’s like they give potential cabbies a personality test and send all the belligerent, competitive, rude drivers to NYC and the pleasant, laid back ones to SF. Many of the cabbies here are middle-aged and older white guys who listen to jazz or classical and have excellent driving skills. They’re a chatty bunch. The rest are the stereotypical recent immigrants, but even they mostly drive well and are polite. It’s nice not having to worry you’ll end up in a road rage incident. I once had a three-block NYC cab ride (I had luggage) and in those three blocks my driver and another cabbie kept trying to cut each other off at signals and were screaming at each other by Penn Station. Guess who didn’t get a tip?