The easiest way to get to South Padre from San Antonio is to go south on I-37, also known as US 281. Next, you will take I-69, also known as US 77, towards Brownsville. At ext 10-B, go right towards Port of Brownsville. Keep straight to get on FM 511, then bear left on TX 550, then merge onto TX 48. Follow the signs to get to the island.