Open steel grid decks are factory assembled, lightweight, and easy to install. They are commonly used to rehabilitate older bridges by being welded to stringers, floor beams, or both. The American Association of State Highway and Transportation Officials (AASHTO) load distribution procedures for open steel grid decks are found to be in error; hence realistic load distribution procedures have been develped to prevent cracking of grid deck bars and plug welds. The research work presented here, however, deals only with the effects of main-bar spacing, direction of main bars with respect to traffic flow, load position, composite action, fatigue effects due to repetitive loads and residual stress build-up in grids during fabrication, braking and accelerating forces, galvanization, and composite action between the deck and stringer. Twenty-six grid deck specimens were tested under static and fatigue loads. Reduction in bending stresses due to composite action is found to be marginal. Allowable fatigue stresses for commercially available welded grid decks are found to be very close to those given for Category E in the AASHTO specifications. However, heavy-duty welded grid decks subjected to fatigue loads have developed no welded cracks after up to 1.5 million cycles. Under fatigue, riveted decks have performed better than the most common welded decks. Finally, welded decks that have been galvanized have a longer service life than decks without galvanization.