  Transportation networks serve as windows into the complex world of urban
systems. By properly characterizing a road network, we can therefore better
understand its encompassing urban system. This study offers a geometrical
approach towards capturing inherent properties of urban road networks. It
offers a robust and efficient methodology towards defining and extracting three
relevant indicators of road networks: area, line, and point thresholds, through
measures of their grid equivalents. By applying the methodology to 50 U.S.
urban systems, we successfully observe differences between eastern versus
western, coastal versus inland, and old versus young, cities. Moreover, we show
that many socio-economic characteristics as well as travel patterns within
urban systems are directly correlated with their corresponding area, line, and
point thresholds.
