75 cuts through Tampa-St. Pete between north and south. That area took a solid five nukes, including a 2MT at MacDill. It probably glows at night, it's so irradiated, and that freeway is at 100 rads/hour JUST FROM MACDILL. That's not even factoring in fallout from hits to St. Pete and Tampa's respective airports, along the same corridor. It'd be a death run. That's why convoys were ruled out. There's no good approach, really, unless you get very enterprising, hug the coast, and get super lucky to find the I-275 bridge over Tampa Bay survived somehow.
https://en.wikipedia.org/wiki/Interstate_75_in_Florida#The_Everglades_and_Southwest_Florida
75 cuts south from Tampa, through Fort Myers and near Naples, then cuts east outside Naples thru the Everglades east to Weston, where it becomes 595 and goes straight to Fort Lauderdale.