I actually found myself telling my dad during our last major snow and ice storm, “no touching downed power lines.” A power line in his neighborhood was lying across the road near his house. He was “helping”.
Power lines tend to come down in severe winter storms, hurricanes, tornadoes and other high wind events. Even though a power line is on the ground it may still be energized. NO TOUCHING! The best thing you can do is call your local energy company or local Department of Public Works. You can also call the police or fire departments.
Is it safe to drive over power lines?
No. It is not safe to drive over power lines. Your car may become energized. I recommend finding an alternate route or waiting for help to arrive and clear the road.
If a power line touches your car[1] (This information comes from Puget Sound Energy)
Note: Once you jump from a car with a power line on it, the danger may not be over. Electricity can spread out through the ground in a circle from any downed line. The voltage drops as you move away from the point of contact. If one part of your body touches a high-voltage zone while another part of your body touches a low-voltage zone, you will become a conductor for electricity. This is why you should shuffle away from the line, keeping your feet close together.
A great resource online for more information: http://www.powerlinesafety.info/RightPanel-001.php
[1] http://www.pse.com/safetyReliability/electricsafety/pages/electricSafety.aspx?tab=1&chapter=5