The　objective　of　this　paper　is　to　present　the　results　of　an　investigation　of　the　dynamic　and　impact　characteristics　of　half-through　arch　bridges　with　rough　decks　caused　by　vehicles　moving　across　them.　Seven　arch　bridges　modeled　as　three-dimensional　structures　with　overall　span　lengths　ranging　from　20　to　200　m　(65.5　to　656.2　ft)　are　analyzed.　The　American　Association　of　State　High-way　and　Transportation　Officiais　Specifications　HS20-44　truck　is　the　applied　vehicle　loading　used　in　the　analysis　and　is　simulated　as　a　three-dimensional,　nonlinear　vehicle　model　with　11　degrees　of　freedom.　Truck　components　include　the　body,　suspension,　and　tires.　The　bridge　deck　surface　is　assumed　to　have　a　＇good＇　surface　roughness　and　is　simulated　using　a　stochastic　process　(power　spectral　density　function).　The　effect　on　impact　factors　of　span　length,　rise-to-span　ratio,　and　vehicle　speed　is　discussed.　The　results　of　the　analyses　show　that　the　impact　factors　of　bending　moment　and　axial　force　will　not　exceed　0.4　and　0.25,　respectively.　The　proposed　impact　equations　are　simple　and　conservative　and　can　be　used　in　the　design　of　half-through　arch　bridges.