A modular bridge deck system supported on a plurality of cooperating girders, comprising: a plurality of deck panels secured together to form a modular bridge deck wherein each deck panel being formed by longitudinally shop friction-stir welding a plurality of elongated, multi-void, extruded aluminum structural elements (12, 312, 412), and a top surface of the respective deck panels and a longitudinal shop-welding form a substantially continuous top surface of the modular bridge deck; wherein each of the aluminum structural elements are the same length and include a top flange having a first end and a second end, and a bottom flange having a first end and a second end wherein the first and second ends (20A, 20B) of the top flange have a thickness that is substantially the same thickness of first and second ends (22A, 22B) of the bottom flange, and each deck panel has at least one extruded aluminum structural end element (18, 518) comprising: a top flange (30,530) longitudinally shop friction stir welded to a corresponding top flange of an outer extruded aluminum structural element of a deck panel; a bottom flange (32, 532) longitudinally shop-welded to a corresponding bottom flange of the outer extruded aluminum structural element of the deck panel; a vertically disposed web (34, 534) integrally formed with the top flange (30, 530) and bottom flange (32, 532); and, wherein the at least one aluminum structural end element (18, 518), including the top flange (30, 530), the bottom flange (32, 532), and the web (34, 534), has a length that is equal to a length of each aluminum structural element. a plurality of deck panels secured together to form a modular bridge deck wherein each deck panel being formed by longitudinally shop friction-stir welding a plurality of elongated, multi-void, extruded aluminum structural elements (12, 312, 412), and a top surface of the respective deck panels and a longitudinal shop-welding form a substantially continuous top surface of the modular bridge deck; wherein each of the aluminum structural elements are the same length and include a top flange having a first end and a second end, and a bottom flange having a first end and a second end wherein the first and second ends (20A, 20B) of the top flange have a thickness that is substantially the same thickness of first and second ends (22A, 22B) of the bottom flange, and each deck panel has at least one extruded aluminum structural end element (18, 518) comprising: a top flange (30,530) longitudinally shop friction stir welded to a corresponding top flange of an outer extruded aluminum structural element of a deck panel; a bottom flange (32, 532) longitudinally shop-welded to a corresponding bottom flange of the outer extruded aluminum structural element of the deck panel; a vertically disposed web (34, 534) integrally formed with the top flange (30, 530) and bottom flange (32, 532); and, wherein the at least one aluminum structural end element (18, 518), including the top flange (30, 530), the bottom flange (32, 532), and the web (34, 534), has a length that is equal to a length of each aluminum structural element. a top flange (30,530) longitudinally shop friction stir welded to a corresponding top flange of an outer extruded aluminum structural element of a deck panel; a bottom flange (32, 532) longitudinally shop-welded to a corresponding bottom flange of the outer extruded aluminum structural element of the deck panel; a vertically disposed web (34, 534) integrally formed with the top flange (30, 530) and bottom flange (32, 532); and, wherein the at least one aluminum structural end element (18, 518), including the top flange (30, 530), the bottom flange (32, 532), and the web (34, 534), has a length that is equal to a length of each aluminum structural element.