When the ice is that thick it becomes possible to actually drive a car or truck across the ice. While driving on ice sounds like something that people would do just for fun, a lot of people drive across frozen lakes for very practical reasons.

For example, there are people who live year-round on islands within these northern lakes. In the middle of winter the only practical way of traveling to the mainland is by driving across the frozen lakes.

Actually, when the lake is frozen two to three feet deep, this is a perfect opportunity for people living on islands to transport large objects onto or off the islands. Say, for instance, you owned a cabin on a small island in the middle of a lake in Michigan. Suppose you decided that you wanted to build an extra room onto the cabin.

Transporting all the building materials onto the island using a boat would take a lot of work and expense. But if you waited until winter, you could easily drive all the building materials across the lake.

How can you tell if a lake is frozen solid enough to drive on? The surest way to know is to wait until several other cars and trucks have safely driven across the ice. Even then, you should always be extra careful when driving across a frozen lake.

It's possible that one section of the lake has currents that prevent the lake from freezing solid. Or there might be a river or stream that brings slightly warmer water into one part of the lake. So even though most of the lake was frozen solid, one section of the lake could have thin ice.

Usually it takes at least two to three weeks of very cold weather before deep ice is formed on a lake. Here in the northern United States, deep ice doesn't form until mid-January, at the earliest. (In northern Canada and Alaska lakes sometimes freeze solid as early as November or December.)