What's making the roads so slick?

There's not much snow in the Twin Cities' air this morning, but the roads are slick and the traffic is creeping.

There are three major elements that cause black ice to form on the roads once the temperatures root squarely below zero. (The wind chill factor at the Grand Marais Airport plunged to minus 54 degrees at 7 a.m. today.)

When the temperatures dip below zero:

• Road chemicals stop working well — and sometimes they don't work at all.

• Car exhaust freezes instantly on the frozen pavement.

• As snow blows across the roads and meets with warm tires: Instant freeze.