Thanks Paul. I saw the ASCE/IBC requirements. Usually, AASHTO requirements are more rigid. But 90 PSF seems to be a bit high for use for a inspection catwalk.
If I cannot find a correct AASHTO reference, I guess I will be designing it for 90 PSF.
For general construction loading, it ranges from 20psf to 75psf, depending of Operational Class (people and equipment using the catwalk), or 300lbs multiplied by the number of workers assumed to be in the location, whichever is greater. See AASHTO Guide Design Specifications for Bridge Temporary Works, Article 2.3.4.3.
For a maintenance catwalk, I would use the 300lbs per worker (including tools). For a public access walkway, I believe it would be the pedestrian live load of 75psf.