North Zone That portion of the state north of a line beginning at the International Bridge south of Fort Hancock; thence north along FM 1088 to State Highway 20; thence west along State Highway 20 to State Highway 148; thence north along State Highway 148 to Interstate Highway 10 at Fort Hancock; thence east along Interstate Highway 10 to Interstate Highway 20; thence northeast along Interstate Highway 20 to Interstate Highway 30 at Fort Worth; thence northeast along Interstate Highway 30 to the Texas-Arkansas state line.
Central Zone That portion of the state between the North Zone and the South Zone.
South Zone That portion of the state south of a line beginning at the International Toll Bridge in Del Rio; thence northeast along U.S. Highway 277 Spur to U.S. Highway 90 in Del Rio; thence east along U.S. Highway 90 to State Loop 1604; thence following Loop 1604 south and east, then north, to Interstate Highway 10; thence east along Interstate Highway 10 to the Texas-Louisiana Line.
