Interstate 345 was part of the original plan for downtown Dallas freeways, which was announced to the public in February 1954. On September 10, 1956, Dallas City Council made an official request to have the freeway designated as part of the national Interstate Highway System. However, the construction of I-35E on the west side of downtown and I-30 on the south side of downtown were higher priority projects, so there was no immediate progress toward construction of I-345.

On October 16, 1964, the U.S. Bureau of Public Roads approved I-345 as part of the Interstate system. The newspaper report stated that the freeway "will carry Interstate Highway 45 signs." It is unknown if the freeway was actually ever signed as I-45; most likely it was not.

Construction began in the summer of 1968, with initial work on the south section from I-30 to Pacific. The first lanes opened on July 9, 1971, allowing westbound I-30 motorists to exit to northbound I-345 and then exit at Main and Elm Streets. All northbound lanes were opened in Spring of 1973, and the project was complete when the southbound lanes opened on August 23, 1973.

So why was this freeway designated as I-345, rather than I-45? I'm still trying to find out the answer to that question. According to the official information on the TxDOT web site, the northern terminus of I-45 has always been at I-30. I-345 was officially designated in October 1964 and has not changed since the original designation. The Interstate status of the freeway would preclude an official designation of US 75. Actual signage on a freeway does not need to adhere to the true designation.

You will not find any I-345 signs along the freeway, or any indications of the official freeway designation. For motorists, I-345 is signed as US 75. Northbound motorists just south of I-30 see a large overhead sign indicating the end of I-45 and the beginning of US 75. About a mile further, a large overhead sign reassures drivers they are on US 75. See the drivers photos for these images.