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 , 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 of the top flange have a thickness that is substantially the same thickness of first and second ends of the bottom flange , and each deck panel has at least one extruded aluminum structural end element comprising: a top flange longitudinally shop friction stir welded to a corresponding top flange of an outer extruded aluminum structural element of a deck panel ; a bottom flange longitudinally shop-welded to a corresponding bottom flange of the outer extruded aluminum structural element of the deck panel ; a vertically disposed web integrally formed with the top flange and bottom flange ; and, wherein the at least one aluminum structural end element , including the top flange , the bottom flange , and the web , 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 , 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 of the top flange have a thickness that is substantially the same thickness of first and second ends of the bottom flange , and each deck panel has at least one extruded aluminum structural end element comprising: a top flange longitudinally shop friction stir welded to a corresponding top flange of an outer extruded aluminum structural element of a deck panel ; a bottom flange longitudinally shop-welded to a corresponding bottom flange of the outer extruded aluminum structural element of the deck panel ; a vertically disposed web integrally formed with the top flange and bottom flange ; and, wherein the at least one aluminum structural end element , including the top flange , the bottom flange , and the web , has a length that is equal to a length of each aluminum structural element . a top flange longitudinally shop friction stir welded to a corresponding top flange of an outer extruded aluminum structural element of a deck panel ; a bottom flange longitudinally shop-welded to a corresponding bottom flange of the outer extruded aluminum structural element of the deck panel ; a vertically disposed web integrally formed with the top flange and bottom flange ; and, wherein the at least one aluminum structural end element , including the top flange , the bottom flange , and the web , has a length that is equal to a length of each aluminum structural element . <EOS>