[biot]

  > A good taxi drive will get you someplace faster than a bad one, will
  > know shortcuts and longcuts, and understands patterns of traffic to
  > avoid them.

A good taxi driver optimizes the ride in order to maximize their fares. The more runs a driver can make between downtown and the airport, for example, the greater their income will be. Besides which, if tips impact the route the driver takes then passengers ought to tip up-front to avoid being "taken for a ride". And if the tipping percentage is to reward efficient driving, how would someone unfamiliar with the city (or drunk, or blind, or ...) know whether they got ripped off or not? Doesn't this ultimately result in tipping someone in order to prevent unethical behavior?