Traffic　flow　at　urban　expressway　interchanges　is　unique,　and　researchers　have　used　the　VISSIM　simulation　model　to　calculate　the　capacity　of　such　interchanges.　In　this　paper,　in　order　to　calibrate　and　validate　VISSIM,　the　measures　of　effectiveness　(MOE)　are　put　forward,　the　confidence　intervals　of　parameters　chosen　in　the　VISSIM　are　calculated,　and　then　the　factors　in　the　interval　are　fine　tuned　to　meet　the　accuracy　of　MOE,　which　is　the　percentage　of　error　between　the　simulated　and　observed　values.　At　last,　the　capacity　of　an　urban　expressway　interchange　in　Guangzhou　is　calculated　based　on　the　proposed　method.　The　validation　results　show　that　the　approach　to　calibration　and　validation　is　feasible.　©　2009　ASCE.