C310 PLT LANDED ON TXWY AT APA. UNAUTH LNDG TXWY LNDG.

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THIS EVENT OCCURRED IN VFR WX; BUT WITH SIGNIFICANT SNOW COVER ON THE GND. ATIS WAS CURRENT WITH THE WARNING THAT THE RWYS WERE COVERED WITH 1/2 INCH OF SNOW AND PATCHY ICE. CLR WITH 20-30 MI VISIBILITY. HOWEVER; THE BRIGHT SUN WITH THE SNOW COVER OBSCURED MANY OBJECTS ON THE GND. MY PLANE WAS ON IFR FLT PLAN FROM IXD TO APA. I WAS UNABLE TO VISUALLY IDENT THE ARPT UNTIL I WAS APPROX 5 NM E OF THE ARPT AT WHICH TIME I WAS CLRED FOR VISUAL TO RWY 17L AND SWITCHED TO TWR FREQ. SHORTLY AFTERWARD; I TURNED R FOR A L DOWNWIND TO RWY 17L. TWR RPTED A CHEYENNE INBOUND FROM THE N AT THE N EDGE OF A LAKE JUST N OF THE ARPT. THE CHEYENNE WAS INBOUND TO RWY 17R. AS I RECALL BOTH MY PLANE AND THE CHEYENNE WERE INSTRUCTED TO LOOK FOR THE OTHER; BUT NEITHER WAS ABLE TO ESTABLISH VISUAL CONTACT WITH THE OTHER ACFT. I TURNED TO L BASE DURING THIS; ABOUT 2 MI NE OF THE ARPT; STILL UNABLE TO ESTABLISH VISUAL OF THE OTHER ACFT. SHORTLY AFTER MY TURN TO BASE; THE TWR INSTRUCTED ME TO TURN STRAIGHT TO THE RWY. I DID SO; ENDING WITH A SHORT FINAL. THE STRUCTURE THAT I IDENTED AS THE RWY WAS MOSTLY COVERED WITH SNOW WITH EXCEPTION OF PATCHY AREAS OF VISIBLE ASPHALT IN THE CENTRAL 1/3. 2 PLANES WERE SITTING TO THE L OF THE APCH END APPEARING TO ME TO BE HOLDING IN THE NORMAL POS TO TAXI ONTO THE RWY. MY LNDG OCCURRED UNEVENTFULLY UNTIL I CAME TO A STOP AT THE END OF WHAT I COULD IDENT AS RWY (THE REST WAS COMPLETELY SNOW COVERED). AT THAT TIME THE TWR INFORMED ME THAT I WAS ON THE TXWY. FACTORS: 1) POOR VISIBILITY OF GND OBJECTS WITH SNOW OBSCURING MANY CRITICAL VISUAL CUES. 2) PLT UNFAMILIARITY WITH ARPT (EVEN THOUGH PROPER CHARTS WERE PRESENT AND HAD BEEN STUDIED). 3) NO INST APCH FOR APCHS TO THE S. 4) POTENTIAL CONFLICTING TFC WITH NEITHER PLT ABLE TO ESTABLISH VISUAL CONTACT WITH OTHER. 5) INSTRUCTION TO FLY DIRECT TO THE RWY RATHER THAN A MORE STANDARD PATTERN. (IF THERE WAS CONCERN ABOUT THE POTENTIAL CONFLICT IN THE CTLR'S MIND; A TURN TO A LONGER DOWNWIND MIGHT HAVE BEEN A BETTER ALTERNATIVE). BOTTOM LINE: GIVEN THE CLR WX AND CURRENT CONDITIONS IT IS QUESTIONABLE THAT THE CTLR COULD FORESEE THE VISUAL DIFFICULTY THAT A PLT MIGHT HAVE. WITH THE CONDITIONS DESCRIBED; I IDENTED WHAT APPEARED TO BE THE RWY AND NEVER DOUBTED THAT THE STRUCTURE IDENTED THROUGH THE SNOW WAS THE RWY. PIC -- GOOD HEALTH; WELL RESTED; CURRENT AND WITH NO STRESS FACTORS. ACFT -- GOOD CONDITION; EQUIP WORKING. NO PAX -- NO COCKPIT DISTRS. ARPT -- MARKINGS OBSCURED BY SNOW; PATCH ICE; NO LOC AVAILABLE FOR APCHS TO THE S.