The R.L Thornton Freeway was initially approved by the Dallas City County in September 1953 from Downtown to Oak Cliff (Marsalis Avenue). Construction on the new alignment for U.S. 67 kicked off in 1955, with it opening as Interstate 35E on May 11, 1959. This included building the Mixmaster Interchange with IH 30.
Further work built Interstate 35E (R.L. Thornton Freeway) in stages from Oak Cliff south to Red Oak as follows: between Marsalis Avenue and Clarendon Drive on January 31, 1962, from Clarendon Drive south to Keist Boulevard on July 6, 1965 and from Keist Boulevard to Laureland Road (Exit 420) on September 21, 1965. These sections of I-35E tied into 1964 opened freeway southward to Bear Creek Road at Desoto and Lancaster. Portions further south in Ellis County were open prior in 1961.2
Origins of the Stemmons Freeway date back to February 1952, when the Dallas County Commissioner Court directed the County Engineer to move forward on an alignment selection for an expressway called Highline-Riverview Road. Further north efforts were underway to expand U.S. 77 (Harry Hines Boulevard) to a four lane roadway between Northwest Highway and the Denton County line. This stretch would tie into the freeway completed in April 1955 between Lewisville and Lake County.2
The alignment of IH 35E would shift west from Harry Hines Boulevard in an effort to reduce costs. This took the future expressway away from built up areas to vacant land next to the Trinity River. TxDOT approved this alignment change in October 1954 and work was well underway by January 1958 on the Stemmons Freeway. The first six miles, between Oak Lawn Avenue near Downtown and the wye interchange (Exit 435) at Hines Park, opened to traffic in December 5, 1959.2
Additional sections of the Stemmons Freeway opened south from Oak Lawn Avenue to the R.L. Thornton Freeway in 1959, from Hines Park north to Northwest Highway in January 1961 and from Northwest Highway to IH 635 on August 15, 1963. Portions of Interstate 35E beyond IH 635 were completed as follows: between IH 635 and the Denton County line on December 14, 1957, through Lewisville as a replacement for U.S. 77 on April 22, 1955, and as an upgrade to freeway standards in 1961 of the four lane highway built for U.S. 77 in 1953 through Corinth. The northernmost section at Denton, including IH 35 north of IH 35W, was finished on June 23, 1959.2