This　study　focuses　on　the　features　and　operational　characteristics　of　dual　left-turn　flow　at　signalized　intersections.　Based　on　the　field　data　collected　in　Beijing　city,　the　saturation　headway　and　saturation　flow　rates　of　dual　left-turn　lanes　at　signalized　intersections　are　studied.　Grand　mean　of　headways,　trimmed　average　value　of　headways,　and　median　value　of　headways　are　computed　and　compared,　and　it　is　found　that　the　trimmed　average　value　of　queuing　vehicle　departure　headway　is　reasonable　to　estimate　the　saturation　headway　and　saturation　flow　rates.　Combined　with　spot-observation　and　data　analysis,　the　influence　of　heavy　vehicles,　lane　width,　left-turn　radius　and　U-turn　behavior　on　the　dual　left-turn　saturation　flow　rates　are　studied.　It　is　recommended　that　heavy　vehicle　equivalency　factors　and　turn-radius　effects　on　saturation　should　be　studied　more　so　that　it　can　be　used　in　practice.　The　study　of　the　effects　of　lane　width　and　U-turn　behavior　on　the　saturation　flow　rates　is　recommended　as　well.　Comparisons　between　dual　left-turn　saturation　flow　rates　and　single　left-turn　lane　saturation　flow　rates　are　also　made.　©　2011　ASCE.