850/70 series TRACS operate only up to 25 mph, doesn't work at high speed. it engages the abs brake system whenever it detects wheel slip (mechanically). it's very intrusive...kinda surprises cause it's so loud...if u get one, try it on a rain day (or wet pavement), turn steering wheel all the way to one direction and stomp on gas with TRACS on. u will notice a noisy repetitive thud. nobody seems to be really complaining about the reliability. personally i've never really found it that useful...didn't really work on fresh snow...even with 3rd gear start and snow tires, still slipped backwards on an incline (good thing there was no one around). i usually leave it off anyway...not sure about others tho.

as for black ice or just ice on highway....850/70 are fwd...so just don't do anything (like hit brakes, downshift, or turn) and just drive thru it.

i believe the new s60-series and the similarly platformed v70-series have newer stability programs that operate at all speeds.