Urban freeways play an important role in urban traffic networks. Compared with highway traffic, urban freeway traffic has different characteristics, such as denser on-and off-ramps, more complex road conditions, and lower velocity limits. Until now, however, there has been no comprehensive analysis of urban traffic flow. In this paper, through an analysis of the density dependence of velocity distribution, we investigate the fundamental velocity–density relationships of urban freeways, compare them with those of highway traffic, and explain them using existing traffic flow theories.