[AF_Blue]

The roads couldn't be pre-treated with brine (SOP) because of the rain that came thru the area the previous day.

Also, a lot of out-of-state visitors were heading home after the New Year's weekend.

[shotgun]

There’s a difference between brine and granular salt applications

You apply brine when it is expected to freeze and get snow. The brine keeps it from sticking hard to the road surface. But it can’t be placed if it is going to rain as you pointed out because it will simply wash away.

Some agencies still use a salt/sand mixture which can provide some breakup and better traction.

For extreme storms on the mountain passes Washington DOT uses a product called Ice Slicer and it will melt away the compacted snow and ice really fast.