High Quality Content by WIKIPEDIA articles! Interstate 45 (I-45) is an intrastate Interstate Highway located entirely within the U.S. state of Texas. It connects the cities of Dallas and Houston, continuing southeast from Houston to Galveston over the Galveston Causeway to the Gulf of Mexico. Interstate 45 is the only intrastate primary Interstate Highway ending in 5 or 0, and its also the shortest primary Interstate highway ending in 5 or 0.