Effectiveness of Taxi Partitions: The Baltimore Case

摘要

This report addresses the controversy concerning the effectiveness of taxi211u001eshields (partitions) by using case study and statistical analysis. It answers 211u001equestion concerning whether or not shields reduce assaults on taxi drivers and by 211u001einference taxi driver homicides. Following a city-wide shield mandate in 1996 211u001ecase study data show that for the City of Baltimore the percentage of shielded 211u001etaxis rose from about 50% in 1995 to 100% in 1996 for the 1,151 licensed 211u001eBaltimore cabs. Comparing the 12-month periods before and after the mandate the 211u001edata shows that assaults on taxi drivers decreased 56%. Data also show that 211u001ebetween the years 1991 when only 5% of the cabs had shields and 1997 when all 211u001edid, assaults decreased 88%. Unless accounted for analytically, confounding 211u001efactor such as annual changes in city crime rates, robberies, unemployment, and 211u001edrug use could also contribute to the assault reduction. However, by comparing 211u001ethe assault rate for a shielded taxi association in 1991 with another similar, 211u001ebut unshielded, taxi association eliminates time varying confounding factors. 211u001eThis analysis shows that an unshielded Baltimore taxi driver in 1991 was five 211u001etimes more likely to experience assaults. Using linear regression to account for 211u001ethe time variation of the factors over the period 1991 to 1997, results indicate 211u001ethat reduced driver assaults correlated most highly with percentage taxis 211u001eshielded. Average case study data, statistical tests and linear regressions show 211u001ethat assaults on taxi drivers are significantly related to shield installation. A 211u001erelated economic analysis yielded a 17-to-1 benefit-to-cost ratio of estimated 211u001esavings from reduced injuries versus the costs of citywide shield installation. 211u001eThus, this study supports the use of shields in Baltimore for the case study 211u001elicensed taxis. The results also argue for shields elsewhere, such as Baltimore 211u001eCounty, and for other cities with conditions similar to those in Baltimore.