Question: Are Interstate Highway 35 and Interregional Highway 35 the Same Road?
One of six major interstate routes going through Texas, Interstate Highway 35 runs North-South just east of downtown Austin.
Answer: An interstate highway system typically connects states and an interregional highway connects cities or regions. Interstate Highway 35 is part of the US Interstate Highway system and it is also an interregional highway connecting Dallas/Fort Worth, Waco, Austin, San Antonio, and other smaller cities in between.
What Austinites Call Interstate Highway 35
During rush hour we call it a parking lot. More formally, in Austin Interstate Highway 35 is most commonly referred to as Interstate 35 (the highway is inferred) and abbreviated I-35 and IH-35. Most states use "I" to abbreviate their interstates. Texas Department of Transportation uses IH. You'll find that Texans and Austinites use both terms and both abbreviations.
Many addresses along IH-35 use Interregional Highway 35, Interregional Highway, or just Interregional as their street address. They all refer to addresses along Interstate Highway 35. Unless reading an address that uses that term, you seldom hear people in Austin refer to IH-35 as Interregional Highway 35.