Theobjectiveofthisresearchistodeterminetheeffectearthquakeshaveontheperformanceoftransportationnetworksystems.Todothis,bridgefragilitycurves,expressedasafunctionofpeakgroundacceleration(PGA)andpeakgroundvelocity(PGV),weredeveloped.Networkdamagewasevaluatedunderthe1994Northridgeearthquakeandscenarioearthquakes.Aprobabilisticmodelwasdevelopedtodeterminetheeffectofrepairofbridgedamageontheimprovementofthenetworkperformanceasdayspassedaftertheevent.Asanexample,thesystemperformancedegradationmeasuredintermsofanindex,"DriversDelay,"iscalculatedfortheLosAngelesareatransportationsystem,andlossesduetoDriversDelaywithandwithoutretrofitwereestimated.