UNANTICIPATED LOSS OF VISIBILITY COMBINED WITH SNOW BUILD UP ON THE RWY BRINGS BE58 TO AN UNPLANNED HALT DURING TKOF ROLL.

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ON THE MORNING OF DEP THERE HAD BEEN ABOUT 1 INCH OF FRESH SNOW ON TOP OF ALL PAVED SURFACES THAT HAD BEEN CLRED THE DAY PRIOR; WHICH USUALLY GIVES IMPROVED (AND GOOD) TRACTION. I DROVE A GOOD PORTION OF THE RAMP AREA; TXWY AND RWY IN MY CAR TO TEST TRACTION AND BRAKING AND FOUND BOTH TO BE GOOD. BRAKES HELD FINE DURING RUN-UP; AND ACFT DID NOT SLIDE OR GIVE ANY OTHER INDICATION OF REDUCED TRACTION DURING TAXI INTO POS ON THE RWY. DURING WARM-UP AND TAXI-OUT; A THIN LAYER (VERY THIN FOG WITH BLUE SKY VISIBLE DIRECTLY ABOVE) OF REDUCED VISIBILITY MOVED IN; ALTHOUGH ASOS CONTINUED TO RPT 10 MI VISIBILITY; 1700 FT OVCST. AS ACFT ACCELERATED DURING THE TKOF ROLL; HOWEVER; THE LAYER BEGAN VISUALLY TO MERGE WITH THE SNOW ON THE RWY AND THE SNOW TO THE SIDE; CAUSING ME CONSIDERABLE DIFFICULTY IN PERCEIVING THE RWY EDGES AT INCREASED SPD. SINCE NO PAVEMENT WAS VISIBLE; I USED THE MARKER POLES THAT WERE PLACED AT INTERVALS TO THE INSIDE OF THE SNOW BANKS TO KEEP THE ACFT CTRED ON THE RWY. THE COMBINATION OF FLAT LIGHT AND WHITE ON BOTH RWY SURFACE AND EDGES GAVE ME THE IMPRESSION OF BEING WELL WITHIN THE PLOWED EDGES WHEN IN FACT THE ACFT HAD SLID TO THE L OF CTRLINE. THE L MAIN CONTACTED HEAVIER SNOW AT THE EDGE OF CLRED RWY WHICH QUICKLY AND UNCTLABLY PULLED THE ACFT TO THE L AND INTO THE SNOW BANK. A CONTRIBUTING FACTOR; IT TURNS OUT; WAS THAT I HAD ASSUMED THE ENTIRE RWY HAD GOOD TRACTION FROM THE ROUGHLY 1/3 (2000+ FT) THAT I DROVE IN MY CAR TO TEST IT BUT IN FACT THERE WAS AN ICE LAYER CONCEALED BY THE SNOW THAT HAD PERSISTED IN THE MIDDLE AREA OF THE RWY. I WOULD RECOMMEND THAT; ONCE WINTER PLOWING COMMENCES; ARPTS IN SNOW COUNTRY NOTAM THE EFFECTIVE WIDTH OF THE RWY; WHICH IS REDUCED EVEN WHEN PLOWED TO THE EDGES (SNOW BANKS CAN CAUSE CONFLICT WITH WINGS). I WOULD ALSO RECOMMEND THAT HIGHLY VISIBLE REFLECTIVE MARKERS BE PLACED AT REGULAR INTERVALS IN THE SNOW BANK; PERHAPS CO-LOCATED WITH LIGHTS. FINALLY; I RECOMMEND THAT TRACTION TESTS DONE WITH TEST VEHICLES EXTEND OVER THE ENTIRE LENGTH OF THE RWY; NOT JUST THE LNDG AND TKOF ZONES; AS BRAKING ACTION CAN VARY SIGNIFICANTLY OVER THE RWY LENGTH.