[3] On the southeast side of the city, US 87 merges with Interstate 10 (I-10); the routes are concurrent for 54 miles (87 km), through San Antonio and the southern part of the Texas Hill Country until an exit at Comfort.

From here, US 87 travels in an almost due northerly heading to Fredericksburg before making a slight turn back to the northwest to Mason, where it merges with US 377.

[4] US 87 is concurrent with I-27 for a majority of its trek to Amarillo, deviating from the interstate route to spur into cities such as Kress, Tulia, and Canyon.

US 385 leaves the route in Dalhart, and US 87 continues on a slight northwesterly path, crossing into New Mexico approximately a mile west of Texline.

[5][6] On March 15, 2022, a bill was signed by President Joe Biden that added the extension of I-27 north to Raton, New Mexico, and south to Laredo to the Interstate Highway System.