To　assess　the　importance　of　bridges　in　road　networks　and　achieve　uniform　traffic　loss　risk　in　seismic　design,　this　paper　introduces　a　novel　bridge　seismic　design　methodology　incorporating　the　Seismic　Importance　Adjustment　Factor　(SIAF)　and　uniform　traffic　loss　risk.　The　key　technical　contributions　are　as　follows:　(1)　defining　SIAF　and　developing　an　integrated　framework　that　couples　seismic　design　with　traffic　loss　risk　assessment;　(2)　proposing　a　calculation　method　for　traffic　loss　risk　that　accounts　for　traffic　demand　variations　during　different　periods　of　the　day,　uncertainties　in　post-earthquake　bridge　repair　times,　and　dynamic　traffic　flow　reassignment　in　post-earthquake　road　networks;　(3)　establishing　design　indicators　for　traffic　loss　risk　and　defining　five　seismic　risk　design　levels　based　on　historical　disaster　data;　(4)　validating　the　methodology　through　case　studies　on　bridges　and　road　networks,　demonstrating　how　SIAF　interconnects　seismic　design　with　risk-based　design　targets　and　adapt　seismic　design　standards　to　varying　network　redundancies.　The　research　demonstrates　that　SIAF　can　quantify　bridge　importance　within　complex　road　networks　and　provide　a　practical　reference　for　the　development　of　seismic　design　standards.　©　The　Author(s),　under　exclusive　licence　to　Springer　Nature　B.V.　2025.