As I mentioned in my previous posts about New York taxis, the system is set up so that legally, the only vehicles that are allowed to respond to street hails are the yellow cabs. The "livery cabs" are legally required to pick up passengers only if they've arranged the service in advance, by contacting the "base." In practice, no matter how many times the city cracks down on livery cabs waiting at informal stands and picking up street hails, they still do it and people still ride.
I've heard allegations that livery cab drivers are less safe than yellow cab drivers. Anecdotally, I've heard about as many horror stories about both and had as many negative experiences with both. I have no idea if anyone's studied crash rates or anything like that with a more systematic method. Even if the livery cabs are less safe, people still ride.
Why do people still ride? Because we want convenience. I regularly travel to a destination that's about twenty minutes by car and forty-five by transit. If I'm short on time I'll take a taxi, but I won't call a car service. The one time I did call a car service, it took fifteen minutes for the car to show up, so I might as well have taken the train. Now I walk five minutes to Queens Boulevard and hail the first taxi that comes along, yellow cab or livery.
This is the reason why every time a functioning transit system has been replaced with one of those "demand response" travesties, demand has gone down. A captive audience like lower and middle-income disabled people have no choice but to arrange their schedules around a ride arranged a day in advance. Anyone else will bike, walk or buy a car. That's what happened in Montgomery, and that's what happens in the "two fare zones" in the outer boroughs that don't have enough carfree households to support a taxi system.
In this age of ubiquitous connections, I could imagine something like the "thumb" in The Hitchhiker's Guide to the Galaxy, that would signal your availability to the nearest car service. That might cut down on cruising, but in practical terms all it would do would be to make hailing a livery cab legal.
In the "inner boroughs," where owning a car is expensive in both time and money, many people will simply risk violating the law by hailing a livery cab, and the drivers will take the greater risk in picking them up. As long as the current system is in place that will continue, unless the city floods the streets with TLC enforcement officers, and we all know they won't spend that kind of money.