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Measuring Racial Discrimination
most of the cars observed (93 percent) were traveling above the posted speed limit, a situation in which police have the ability to stop almost any car for speeding. Lamberth clearly believes that racial differences in stop rates when almost everyone is speeding must reflect racial bias. This conclusion, however, rests implicitly on the proposition that speeding was the only basis for stopping cars on the Maryland highway (although one could look only at those stopped for speeding) and that there was virtually no difference in the distribution of speeds for white and black drivers. Lamberth’s own data show that whites were more likely than blacks to be driving at the lawful speed on I-95 in Maryland. (Specifically, 7.9 percent of the white drivers observed in Lamberth’s study, but only 3.6 percent of the black drivers, were not speeding.) Indeed, a subsequent study conducted on the New Jersey turnpike using radar devices and cameras to determine car speeds and the race of drivers revealed that blacks did drive at very high speeds more often than whites, which would likely cause them to attract more attention from police.6
Yet even if racial differences in the rate of stopping motorists on Maryland highways can be explained by differences in driving behavior, the racial disparities in rates of search for illegal activity conditional on being stopped appear to be quite large. The Maryland State Police reported stopping and searching 823 drivers on I-95 during the observation period of Lamberth’s (1996) study; 73 percent of those drivers were black and only 20 percent white (the remaining drivers were other racial minorities). Yet blacks accounted for only 18 percent of the speeding drivers who were eligible to be stopped on I-95 (from Lamberth’s data), compared with 73 percent of those who were actually searched (from the police data). Lamberth (1994) obtained similar results in his New Jersey study.
Assessment of traffic-violating behaviors. Few studies have determined whether traffic-violating behaviors vary by race. Lamberth (1994, 1996) tried to establish base rates in his studies; however, he did not determine the severity of violating behaviors. Severity in the case of speeding involves both the rate of speed of a driver and the speed at which state police issue citations, which can differ from state to state. For example, if police in a state routinely allow drivers to exceed the posted speed limit by 10 mph, researchers would need to establish the rates at which different racial groups
The study found that in the southern part of New Jersey, where claims of racial profiling had been most common and where the speed limit was 65 mph, 2.7 percent of black drivers compared with 1.4 percent of white drivers drove faster than 80 mph. The racial disparity was even greater for those driving faster than 90 mph. On the other hand, the study did not find any racial differential in speeding in northern New Jersey areas having speed limits of only 55 mph (Kocieniewski, 2002).