On the southeast side of the city, US 87 merges with Interstate 10 (I-10), where it continues through San Antonio as a co-signed, concurrent route for 54 miles , until an exit at Comfort, where the highway once again picks up its own signage and continues on, in an almost due northern heading to Fredericksburg, before making a slight turn back to the northwest to Mason, where it merges with US 377.