In a deck of simply span bridge of 24ft length and width of 34ft
closed as unclear what you're asking by Michael Karas♦, Tester101 Jun 2 '17 at 10:16
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Anything that big and carrying a load (you said "traffic") is deep in the "licensed structural engineer" category. Don't ask about it on the internet, find someone with a suitable university degree, license from the local authorities, and quite a bit of experience building bridges.
No, this person will not be cheap. But neither will that bridge.