The Seattle Times has a piece this morning on the West Seattle Viaduct crash and closure yesterday. Says SDOT thinks the anti-icer compound they put down a bit after noon didn't crystallize on the pavement quick enough due to the temperature being above freezing, so it stayed in gel form and might have been slippery. That's all they and the police can think caused the subsequent crashes.
A friend's bike went out from under him a couple of years ago while we were doing Zoo Hill repeats, at the right angle by the school up top. We couldn't see anything that would have caused him to fall, except the tracks of de-icer application done by Bellevue. No way it was that stuff, we thought. Well, maybe now we know. And there's something else to be aware of while out on the roads, and especially while descending. If de-icer gel is laid down when the weather is not truly freezing, it will still crystallize but not very quickly. Another caution light for the situationally aware.