Surprised Philadelphia didn't make it, being a crowded city with a large city limit population. It would be interesting to see how urban areas stack up. A 6 square mile suburb of Boston makes the top 10. The dense city area around Boston is so fractured into politically separate entities, but the area has more cabs than anywhere I've seen in the US outside NYC and Boston. Houston is single passenger car hell, but enormous city limits work in sheer numbers for the statistic.