The　rapid　development　of　expressways　has　led　to　an　increasing　number　of　place　names　that　must　be　displayed　on　road　guide　signs.　As　a　result,　multi-board　guide　signs　have　been　increasingly　set　up　on　expressways.　The　main　aim　of　this　study　was　to　analyze　the　effect　of　the　directional　road　sign　displayed　on　multi　and　single-board　signs　on　driver　mental　workload　and　behavior.　32　participants　including　16　females　(mean　age　=　24.7　years,　standard　deviation　=　1.9　years)　participated　in　the　experiment　and　completed　3　driving　simulation　scenes.　The　setting　of　each　scene-sign　board　was　different:　1　board,　2　boards,　and　3　boards.　The　driver　needed　to　reach　the　designated　destination　according　to　the　guidance　of　the　road　signs.　Eye　tracker　was　used　to　measure　the　fixation,　saccade　and　electroencephalogram　(EEG)　was　used　to　measure　the　alpha　(8-13　hz)　band　absolute　power　in　different　signage　scenarios.　There　are　two　major　findings　of　the　study.　First,　when　the　number　of　place　names　is　less　than　or　equal　to　7,　the　multi-board　sign　generates　more　mental　workload　than　the　single-board　sign　does.　The　alpha　band　power　of　the　driver＇s　frontal　area　under　the　multiple　boards　is　lower　and　affects　driving　performance　(the　deceleration　is　greater).　Second,　when　the　number　of　place　names　is　more　than　7,　there　is　no　significant　difference　in　the　effect　on　mental　workload　whether　multi　or　single-board　sign　is　used.　However,　compared　to　the　single-board　sign,　drivers　in　the　case　of　multi-board　sign　are　likely　to　reduce　the　fixation　duration　and　increase　the　number　of　saccades.　The　results　suggest　that　it　is　not　necessary　to　use　multi-board　signs　when　the　number　of　place　names　is　less　than　7.　These　findings　provide　more　safety　considerations　for　the　setting　of　multi-board　guide　signs　in　the　future.