We used Dyna map data from TeleAtlas (Global Crossroads, Boston,MA) for 2000 as the base road network configuration. The highway category was based on combining two categories from the Dyna map database: (1) primary roadways without limited access (Feature Class Code — FCC A1); and (2) primary roadways with limited-access or state highways (FCC A2). Major roadways were created from the Dyna map secondary and connecting roadway data category (FCC A3).The population data and corresponding boundary files were at the census tract level from U.S. Census Bureau for 2000.