A side underride system configured to be coupled to a trailer is disclosed. The side underride system comprises a support system configured to be positioned below the trailer to provide side underride protection. The support system includes a cable system and a brace system. The cable system is configured to couple to the trailer. The brace system includes a plurality of cross-braces that each extend at least partially across a width of the trailer, are spaced apart at intervals along a length of the trailer, and are configured to capture the cable system.