In　order　to　assess　the　vehicle　load　carrying　capacity　of　existing　bridges　on　the　national　highway　G103　in　Beijing,　the　vehicle　load　model　for　the　practical　traffic　flow　conditions　needs　to　be　determined.　Based　on　the　traffic　axle　load　data　measured　by　the　weigh-in-motion　system　and　the　methods　proposed　by　General　Code　for　Design　of　Highway　Bridges　and　Culverts　(JTG　D60-2004)　and　Code　for　Design　of　Highway　Reinforced　Concrete　and　Prestressed　Concrete　Bridges　and　Culverts　(JTG　D62-2004),　the　vehicle　load　parameters　under　practical　traffic　flow　conditions　are　investigated.　A　typical　6-axle　vehicle　model　with　a　2-1-3　axial　pattern　is　proposed　by　using　the　statistical　analysis　of　total　weight,　axial　weight,　etc.　The　live　load　effects　of　Daliushu　No.　2　Bridge,　one　highway　bridge　on　the　national　highway　G103,　are　analyzed　using　the　proposed　model　and　compared　to　the　vehicle　load　model　given　in　the　Chinese　code.　The　results　show　that　there　are　great　differences　in　the　vehicle　load　parameters　and　the　live　load　effects　from　the　proposed　vehicle　load　model　increased　by　20-50%　compared　with　the　model　given　by　the　code.　The　overweight　vehicles　are　potential　threats　to　the　safety　of　existing　bridges.