Its southern (western) terminus is in Eagle Pass, at the Rio Grande (Río Bravo), where it continues into Piedras Negras, Coahuila, as Mexican Federal Highway 57.

The highway travels eastward through Eagle Pass on Garrison Street.

[3] US 57 continues eastward through Batesville and unincorporated areas of Zavala and Frio counties, intersecting several Farm to Market roads, before reaching its eastern terminus at Interstate 35 (I-35) southwest of the town of Moore.

From 1942 to 1964, its eastern half was reassigned to Farm to Market Road 394 (FM 394).

However, Mexican Federal Highway 57 travels south to Mexico City, so the unusual directional signing prevents confusion.