Prior　safety　evaluations　of　interchange　merging　areas　have　mostly　focused　on　traffic　conflicts　and　operating　speeds,　without　considering　how　these　factors　can　influence　the　driver　workload.　Researches　regarding　the　level　of　driver　workload　have　largely　concentrated　on　urban　roads,　tunnel　sections,　and　basic　freeway　segments,　without　considering　the　impact　of　merging　traffic　flows　on　safety.　Therefore,　this　study　has　investigated　how　merging　vehicles　can　impact　through-driver　workload　and　safety.　Three　independent　field　experiments　were　conducted　on　freeways,　involving　18　drivers　and　17　interchanges.　The　results　showed　that　the　vehicles　merging　onto　freeway　impact　driver　workload　and　driving　performance,　generating　potential　risk　that　cannot　be　ignored.　Merging　into　the　mainline　traffic　flow　increases　the　through-driver　workload　to　a　higher　level　or　even　exceeds　the　safety　threshold,　despite　there　being　better　geometrical　conditions　of　interchanges　than　those　of　basic　freeway　segments.　When　the　volume　of　merging　vehicles　exceeds　564　pcu/h　or　the　traffic　saturation　is　above　0.485,　driver　workload　rises　above　the　safety　thresholds　and　the　driving　risk　is　elevated,　which　potentially　would　lead　to　crashes.　This　study　offers　insights　for　more　effective　segment　division　of　operating　speed　prediction,　and　dynamic　risk　management　with　regard　to　interchange　safety.