THE PLT'S ORIGINAL DESTN WAS LEXINGTON, KY, HOWEVER BETWEEN BLUEFIELD, KY AND LEXINGTON, HE AMENDED HIS DESTN TO INDIANAPOLIS, IN. THE PLT STATED THAT FUEL CONSUMPTION WAS CALCULATED AS 7.1 GPH, BUT HE DID NOT TAKE INTO CONSIDERATION THE CESSNA 172 TIME/FUEL TO CLIMB CHART OR THE 10% VARIANCE FOR ACFT/ENGINE CONDITION, ACCESSORY CONDITION, OR TURBULENCE. FUEL CONSUMPTION CALCULATIONS AT 7.8 GPH (7.1 GPH CRUISE CONSUMPTION RATE + 10% VARIANCE) INDICATE THAT FOLLOWING TAKEOFF AND CLIMB, THE REMAINING FLT ENDURANCE WAS ABOUT 5.1 HOURS. THE PLT DEPARTED RALEIGH-DURHAM, NC AT 1530 EST AND HE REPORTED FUEL EXHAUSTION TO THE INDIANAPOLIS INTERNATIONAL APPROACH CONTROL AT 2030 EST. THE ACFT COLLIDED WITH AN OVERPASS SUPPORT STRUCTURE WHILE LANDING IN THE EASTBOUND LANES OF I-74, ABOUT FOUR MILES EAST-SOUTHEAST OF SHELBYVILLE, IN. AFTER THE ACCIDENT, A TOTAL OF APPRX ONE CUP OF FUEL WAS DRAINED FROM THE ACFT WING SUMPS AND GASCOLATOR.