The western terminus of FM 78 is in Bexar County, near Fort Sam Houston and the southern end of the concurrency of Interstates 35 and 410 in San Antonio. Access to FM 78 is available from IH 35 Exit #162 and from IH 410 Exit #31A and #32. Heading in a northeasterly direction, the route briefly enters Kirby before reentering San Antonio. FM 78 crosses into Converse and then Universal City, where it has a junction with Loop 1604. Outside of the loop, the route borders the north edge of Randolph Air Force Base. FM 78 then enters Guadalupe County and passes through Schertz, Cibolo, Santa Clara, Marion, and McQueeney. The highway then crosses the Guadalupe River and enters the city ofSeguin. It has a junction with IH 10 at Exit #607, an interchange it shares with SH 46. FM 78 continues eastward into Seguin along West New Braunfels Street and then southward on 8th Street before reaching its terminus at US 90. FM 78 provides a connection between central San Antonio and Randolph Air Force Base. It also provides an alternate route between Seguin and portions of the northeastern San Antonio metropolitan area. Between San Antonio and Cibolo, FM 78 is a four-lane road, dropping to a two-lane road until McQueeney, before becoming a four-lane divided route to IH 10/SH 46.
History
Present-day FM 78 is part of what was the much longer original SH 3 designated in 1917. Most of this route was usurped by US 90 during the mass redescription of the state's highway system in 1939, while FM 78 was designated on August 3, 1943 over the portion of SH 3 which ran from FM 25 in western Seguin to SH 218 at what was then known as Randolph Field. On February 14, 1947, the western terminus was extended to Loop 13, and the extension to IH 35 occurred on August 1, 1977. The route was extended eastward into Seguin along New Braunfels and 8th Streets to its current terminus at US 90 on September 26, 1979. On June 27, 1995, the mileage of the section from IH 35 to FM 3009 in Schertz was officially transferred to Urban Road 78. On November 15, 2018, Urban Road 78 became part of FM 78 again. The UR 78 designation was never signed as such. An older segment of FM 78 became Loop 539 on September 26, 1996, when the alignment of FM 78 in southern Cibolo was shifted to the south, while FM 78 was rerouted over the old Loop 539. Loop 539 was cancelled and given to the city of Cibolo on November 30, 2014.
