What to know about the dangers of black ice

Black ice is clear so it's hard to see the difference between a wet road & ice.

As Wednesday's nor'easter leaves slippery black ice in its wake, here's a closer look at why black ice is so dangerous.

Black ice occurs when liquid freezes on a black roadway. The ice is completely clear, so it's difficult for motorists and pedestrians to distinguish the difference between a wet roadway and slippery ice.

ABC News' Gio Benitez carefully walked along black ice in Saddle Brook, New Jersey, this morning.

"If you've tried driving on roads that have this black ice, you will see that you will lose control and sometimes you can't even see it," Benitez said. "You really need to look for that sort of reflective sheet of ice."

Black ice tends to form in the shaded areas of the roadway and on bridges and overpasses that freeze first and melt last, AAA National spokeswoman Jeanette Casselano told ABC News earlier this winter.

It takes a vehicle nine times longer to stop in ice and snow compared to clear conditions, added AAA Northeast spokesman Robert Sinclair.

While salting can help prevent black ice from developing, the effectiveness of the salt goes down once temperatures fall below 20 degrees.

Here are some of AAA's tips for driving in winter weather:

--Avoid tailgating.
--Don't use cruise control on slippery roads.
--Slow down immediately when you see brake lights ahead.
--Don't slam on your brakes.
--If your car skids, continue to steer in the direction you want the car to go.

ABC News' Erin Keohane and Emily Shapiro contributed to this report.