Didn't notice the bottom one wasn't 5. But if 2 was 20T and 4 was 60K I would assume 80K would be legal with proper bridged axles. That being said there is no gross limit indicated and would hate to end up at the bottom.
Then you need to break out some paper and your crayons and add to the sign. Seriously, I think they intended single vehicle, combination vehicle, and doubles. And considering the doubles is only 1T higher than the middle, I would assume GVWR for a 5 axle vehicle us 29T. I think you're in IL, so there is a length restriction as well so even if you ignore the GVWR and focus on actual wieght it wont matter if you're under 29T, you'll still get a ticket. You can fight it on signage, but doubt you'd win.
It’s in southeast Nebraska. But there are no detour signs anywhere around telling you to take a different route. The only signs showing the limits are right next to the bridge within a mile.