A CL65 FO IS CONCERNED WITH XING RWY 18-36 WITHOUT A CLRNC AFTER CLRING RWY 5 AT TXWY R AT CLE ARPT.

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AFTER LNDG ON RWY 5R AT CLE; WE EXITED TO THE R ONTO TXWY R. AS THE CAPT BEGAN HIS TURN TO EXIT RWY 5R; HE CALLED FOR FLAPS UP AND AFTER LNDG CHK. WHILE ACCOMPLISHING THE CHKLIST ITEMS; I LOOKED UP TO SEE US XING A HOLD SHORT LINE. I QUICKLY LOOKED L AND R AND SAW NO TFC MOVING ON THE RWY WE WERE ABOUT TO CROSS BUT THERE WERE ACFT PARKED ON THE RWY S OF OUR XING POINT. I VOICED MY CONCERN ABOUT OUR TAXI RTE TO THE CAPT AND WE DETERMINED THAT THE RWY WE HAD CROSSED WAS RWY 18/36 WHICH WAS NOTAMED CLOSED ON THE ATIS. I CALLED GND TO NOTIFY WE WERE CLR OF RWY 5R; NOT MENTIONING RWY 18/36; AND THEY ISSUED US TAXI INSTRUCTIONS TO THE GATE. ALL OF THIS OCCURRED WITHIN ABOUT 12 SECONDS TIME. HAVING HAD THE OPPORTUNITY TO REVIEW THE CLE ARPT DIAGRAM; I'M NOT EVEN SURE THAT THERE IS PHYSICALLY ENOUGH SPACE ON TXWY R BTWN RWY 5R AND RWY 18/36 TO EXIT RWY 5R AND KEEP THE AIRPLANE BTWN THE PROTECTED AREAS FOR BOTH RWY 5R AND RWY 18/36. IF IT IS NOT POSSIBLE; THEN A PLT MAY EXIT RWY 5R AT THE FIRST AVAILABLE TXWY AND HAVE TO CHOOSE BTWN BLOCKING THE ACTIVE RWY OR POKING INTO THE PROTECTED AREA FOR RWY 18/36. IN OUR CASE; ATC MADE NO COMPLAINTS.