One of the reasos could be 'black ice', when snow got melt down but frozen again as ice. Usually it happens in temperature around 0c.
But the RX350 likely had problem too as other vehicles stopped with no problem.
关键问题可能是2010款的RX350没有“刹车是爷”功能。(For 2011, the only notable change to the RX is its standard brake override system)
http://usnews.rankingsandreviews.com/cars-trucks/Lexus_RX-350/