The story
The Texas Legislature created the Texas Highway Department in 1916 to administer federal highway construction and maintenance. In 1975, its responsibilities increased when the agency merged with the Texas Mass Transportation Commission, resulting in the formation of the State Department of Highways and Public Transportation.
In 1986, the department started using "Don't Mess with Texas" as its slogan to reduce littering on Texas roadways, as part of a statewide advertising campaign. The phrase was prominently shown on road signs on major highways, as well as in television, radio, and print advertisements. The slogan is still in use and remains very popular.
In 1991, the Legislature combined the State Department of Highways and Public Transportation, the Department of Aviation, and the Texas Motor Vehicle Commission to create the Texas Department of Transportation (TxDOT).
In 1997, the pre-existing Texas Turnpike Authority (TTA) was divided into two successor agencies: the North Texas Tollway Authority took responsibility for TTA assets in four North Texas counties, while the Turnpike Authority Division of Texas DOT was given jurisdiction over toll facilities in the rest of the state.
In 2005, as a result of House Bill 2702 the rail oversight functions of the Texas Railroad Commission were transferred to TxDOT.
In 2009, the Texas Department of Motor Vehicles was created by the state legislature, taking over some functions from TxDOT.
In 2016, the Texas A&M University Press published MILES and MILES of TEXAS; 100 Years of the Texas Highway Department.
From Wikipedia’s article on Texas Department of Transportation, shared under CC BY-SA 4.0.5