I lived in Austin in the early 80’s and they always called it IH-35. (Interstate Highway)
They no longer call Interstates IH?
The labels/signs still say that sometimes but mostly it is “I-{number of highway}” in Texas. If the I prefix is even used, which is a coin toss.
California dropped the I prefix and just calls them by number, but puts “the” in front of them : “The 101” “The 5”, etc., etc.
Maybe Killeen has a Yankee infestation nowadays.