Urban　interchanges　contain　both　saturated　traffic　flow　and　unsaturated　traffic　flow.　Their　traffic　characteristics　are　significantly　different　from　signalized　intersections　and　unsignalized　intersections.　On　the　foundation　of　iterative　observation　and　research　of　traffic　flow　characteristics　of　a　Beijing　cloverleaf　interchange,　this　paper　puts　forward　a　study　on　urban　cloverleaf　interchanges.　Traffic　flow　at　urban　interchanges　is　unique;　combining　actual　data　and　calibration,　researchers　used　the　VISSIM　simulation　model　to　calculate　the　capacity　of　the　Anhua　Bridge.　The　capacity　of　the　whole　interchange　is　analyzed　by　simulation　experiments,　and　the　relationship　between　the　whole　interchange　capacity　and　the　turning　vehicle　proportions　is　put　forward;　with　the　increase　of　turning　vehicle　proportions,　the　whole　traffic　capacity　of　the　interchange　decreases　constantly.　The　conclusion　can　be　used　for　decision-making　on　planning,　design,　and　management.　©　2012　American　Society　of　Civil　Engineering.