were asphalt, were gravel, shell or stone, and were clay or soil. In 1951, a section of the Gulf Freeway (now I-45) opened, becoming Texas' first urban freeway. In 1957, the state began receiving federal funding for the construction of the Interstate Highway System. The first section of Interstate Highway from county line to county line to open in the state was a section of I-35 in Bexar County. By 1967, the highway system controlled of highway. In 1984, US 66 was replaced by I-40 and the US 66 designation was removed from the state highway system the following year. In 1992, the of Interstate Highway System in Texas was completed with the opening of a section of I-27. In 1997, the Texas Turnpike Authority was merged with TxDOT and independently, the North Texas Turnpike Authority became responsible for toll projects in Collin, Dallas, Denton, and Tarrant counties. Types of highways Interstate Highways The Interstate Highway System in Texas covers and consists of ten primary highways, seven auxiliary highways, and the splitting of both Interstate 35 (I-35) and Interstate 69 into multiple letter-suffixed branches. The Interstate Highway with the longest segment in Texas is I-10 at . The shortest in the state is I-110 at . The construction of the Interstate Highway System in Texas actually began well before these routes were designated as Interstate Highways. A stretch of the Gulf Freeway (I-45) between Galveston and Houston was opened in 1951, eight years before it was designated I-45. It was also the first urban expressway in Texas. In 1962, of I-35 opened in Bexar County, the first section of Interstate Highway to open from county line to county line in a large metropolitan area. Portions of I-10 west of San Antonio took much longer to complete due to the vast open spaces and lack of nearby labor. The majority of the construction of this section of I-10 occurred in the 1970s and 1980s and was complete by the early 1990s. The section east of San Antonio was completed 20 years earlier in 1972. The opening of a section of I-27 in 1992 completed the Interstate Highway System in Texas. Construction is ongoing for an extension of I-69 southward from its original terminus in Indiana through Texas to the Mexican border. When built, I-69 will extend about across Texas, from the Louisiana state line in the Texarkana–Shreveport area to South Texas.