The Interstate Highways in Texas cover 3,233.4 miles (5,203.7 km) in the state. The freeways are maintained by the Texas Department of Transportation (TxDOT) as the state agency responsible for all state highways, including the Interstate Highways in Texas. There are ten primary routes, six auxiliary routes and two branches of Interstate 35 (I-35) as it splits into eastern and western branches near Fort Worth and Dallas. The Interstate Highway with the longest segment in Texas is I-10 (interchange with I-45 pictured) at 878.6 miles (1,414.0 km), making it also the longest continuous untolled freeway under a single authority in North America; the shortest in the state is I-110 at 0.9 miles (1.4 km). The construction of the Interstate Highway System in Texas actually began well before these routes were designated as such. Part of the Gulf Freeway between Galveston and Houston was opened in 1951, eight years before it was designated I-45. The opening of a short section of I-27 in 1992 completed the system. Planning is ongoing for a proposed extension of I-69 southward from its current terminus in Indiana through Texas to the United States–Mexico border, the first segment of which was added in December 2011. (Full list...)