 The Dallas–Fort Worth and Houston metropolitan areas number about 6.3 million and 5.7 million residents, respectively.Three interstate highways—I-35 to the west (Dallas–Fort Worth to San Antonio, with Austin in between), I-45 to the east (Dallas to Houston), and I-10 to the south (San Antonio to Houston) define the Texas Urban Triangle region.The region of contains most of the state's largest cities and metropolitan areas as well as 17 million people, nearly 75 percent of Texas's total population.