I have 43' shop welded truss.
I usually only go less than 40' for maximum length.
When can I get information for maximum lengths for beams transportation within US?
43' should be okay, they have regular trailers longer than that.
For true oversize stuff, it becomes an economic question, you see them hauling the precast bridge girders all the time, maybe 100' long? They're permit loads, require escorts, but can be done. Go to Youtube, look for "heavy haul", etc, for examples.
The best thing is to ask a fabricator. In NYC and Long Island the rule of thumb is 100' or 100 Tons. North of the city, shipping is a bit easier. On one project a fabricator was able to truck 140' steel tubs.