To address the issue of bridge collisions induced by earthquakes, seismic vulnerability curves for the overall system and individual components of conventional and irregular box girder highway bridges, with and without collisions, were developed and compared based on nonlinear time history analysis using the OpenSees finite element software. Four damage states, ranging from minor to severe, were established. The fragility function was employed to elucidate the interaction between structural irregularities and collisions between the bridge deck and the abutment on the seismic vulnerability of multi-span box girder highway bridges. A conversion coefficient, r_p, was introduced to quantify the impact of collisions on the vulnerabilities of bridge components and the overall system. Traditional analysis methods, including static and simplified analyses, alongside technical seismic models, were applied to adjust the vulnerability values associated with collisions and irregularities. The findings reveal that collisions exert adverse effects on all structural components. As the damage level increase, the variability in RP values for the ductility of bridge columns and anti-falling beams also increase. Specifically, for earthquake number 2, the r_p values under damage conditions are 0.95 for mild(DC₁) and 1.02 for moderate (DC₂). Under pulse type seismic motion, collisions significantly increase the degree of damage to engineering demand parameters (EDP). For earthquake number 3, the average r_p value for foundation translation was 0.71 with collisions and 0.57 without, highlighting the significant destructive influence of collisions on foundation translation. By comparing the median values across all categories, it was observed that the median values for earthquake numbers 3 and 1A were lower than those for earthquake numbers 2 and 1B, indicating that collisions caused more severe damage under lower ground motion intensities. This study provides a valuable reference for seismic bridge design, offering insights to improve design specifications, enhance the seismic performance of bridge structures, and deliver significant engineering and practical applications.