This Taxi Brakes for Tips

Cab drivers' reluctance to pick up minority passengers is often attributed to "drive-by racism." But according to one study, it is the tipping habits of passengers—not simply driver prejudice—that may explain the phenomenon. Yale University researchers analyzed more than 1,000 Connecticut taxi rides after drivers recorded each passenger's fare, tip and race.

The average white passenger tipped about $1.54, while the typical black passenger tipped $1.02. Forty percent of African-American passengers and 34 percent of Hispanic passengers stiffed the driver, compared to 11 percent of Caucasian passengers.

Surprisingly, black drivers may have the least incentive for picking up passengers of their own race: Black passengers tipped black drivers nearly 70 percent less than they tipped white drivers. And black drivers were 80 percent more likely than white drivers to receive no tip at all from passengers of any race. Yale University law professor Ian Ayres says a tipping bias may be why many cabbies pass up minority customers.

The link between income and race likely explains much of the disparity, says Ayres. In any case, drivers appear to make inferences based on external factors. "Cab drivers can't see how rich you are when they pull up to the curb," he says. "What they can see is your race and a few other variables."