Passenger　Car　Equivalent　(PCE)　is　a　unit　used　to　represent　the　impact　of　a　large　vehicle　on　a　road　by　expressing　it　as　the　number　of　equivalent　passenger　vehicles.　This　paper　focuses　on　estimating　the　PCE　of　various　sized　heavy　vehicles　in　roundabouts　with　respect　to　different　entry　flow　rates.　A　single-lane　roundabout　was　tested　under　predefined　mixed　traffic　and　demand　scenarios　in　VISSIM　micro-simulation　environments.　The　individual　and　group　behavior　of　four　separate　heavy-vehicle　types　were　tested:　single-unit　trucks,　buses,　small　semitrailers,　and　large　semitrailers.　The　obtained　PCE　values　were　found　to　be　on　average　lower　than　those　suggested　in　the　United　States　guidelines　for　roundabouts.　The　estimated　PCE　values　for　heavy　vehicles　in　mixed　traffic　conditions　are　1.30　for　single　unit　trucks,　1.40　for　small　semitrailers,　1.60　for　buses,　and　1.70　for　large　semitrailers.　Additional　factors　such　as　varying　inflow　(balanced,　unbalanced,　and　congested　traffic)　show　direct　influences　on　the　PCE　values.　The　PCE　value　under　these　conditions　ranged　from　1.25　to　1.75　for　smaller　vehicles　(single-unit　trucks,　buses,　and　small　semitrailers)　and　1.45–2.10　for　larger　heavy　vehicles　(large　semitrailers).　A　general　equation　was　developed　based　on　the　data　to　relate　vehicle　proportions　and　heavy-vehicle　reduction　factors　that　would　be　useful　for　professionals　to　analyze　the　operational　performance　of　roundabouts　with　better　accuracy.　©　2019　Pajecki,　Ahmed,　Qu,　Zheng,　Yang　and　Easa.