PLT WAS IN LEVEL CRZ FLT AT NIGHT WHEN HE OBSERVED SPARKS AND FLAME COMING FROM THE ENG COWLING. SHORTLY THEREAFTER, THE ENG BEGAN RUNNING ROUGH AND THEN SEIZED. AFTER DECLARING AN EMERGENCY AND BEING CLEARED STRAIGHT IN TO A RUNWAY ABOUT 28 MILES AWAY, THE PLT DECIDED THAT HE COULD NOT MAKE THE RWY AND EXECUTED AN EMERG LNDG ON AN UNLIGHTED STRETCH OF INTERSTATE HWY. DRNG THE LNDG ROLL, THE RT WING STRUCK A GUARD RAIL AND THE ACFT VEERED RT, COLLAPSING THE MLG. INVESTIGATION REVEALED THAT THE NO. 3 CYL HAD SEPARATED INTO 2 PIECES AS A RESULT OF A FATIGUE CRACK THAT HAD INITIATED AT THE INNER DIAMETER OF THE CYL. THE CAUSE OF THE FATIGUE INITIATION COULD NOT BE DETERMINED. EVIDENCE INDICATED THAT THE CYL FATIGUE CRACK HAD BEEN THERE FOR SOME TIME, MORE THAN THE 26 HRS THAT HAD ELAPSED SINCE THE LAST 100 HR INSP.