"It's also important to remember that street taxi service is not a particularly efficient market system. In the norms of the taxi market, you cannot in fact be choosy about what cab picks you up (even if you could, there's virtually no information available to you when a cab pulls up)."

The technology to do this already exists. If taxi drivers could see where the demand is, and riders could see feedback on drivers, it would solve this problem. Of course technology alone is not enough. To achieve this, you'd need to disrupt the status quo, a part of which is laws that disallow "street hails" of taxis that don't have medallions.