>> Only "medallion taxicabs," those painted in distinctive yellow and regulated by the TLC, are permitted to pick up passengers in response to a street hail. The TLC also regulates and licenses for-hire vehicles, known as “car services” or “livery cabs,” which are prohibited from picking up street hails (although this rule is less often enforced in the boroughs outside Manhattan)[44] and are supposed to pick up only those customers who have called the car service's dispatcher and requested a car.

Those $1m medallions are just an iPhone (or mobile web) app away from a crash. In fact, I think there's already some company that does this.