Ask a Trooper: Clearing the air on foggy driving

Sgt. Jesse Grabow, Minnesota State Patrol

Question: Can you give some advice on driving in fog? The fog became one car-length dense the other day and it became a dangerous situation.

Answer: Driving when the weather limits your visibility can be a challenge for all of us on the road. You can reduce your chances of being involved in a crash by following a few safety tips.

Minnesota law says that every vehicle on a roadway shall display lighted headlamps, lighted tail lamps, and illuminating devices from sunset to sunrise. The law also applies when it’s raining, snowing, sleeting, or hailing and at any time when visibility is impaired by weather or insufficient light, at a distance of 500 feet ahead.

Basic automatic headlights work through sensors which detect how much light is outside. These sensors are located on the dash of the vehicle. The headlights turn on when the sensors detect a certain level of darkness or the level of ambient light.

The problem is there are limitations to automatic headlights. Sometimes they do not turn on during heavy rain, snow or fog, as the light sensor still detects some light.


I see many drivers that fail to physically turn on their headlights, which will also activate the rear taillights and marker lights. Drivers might assume the sensors will activate all of the vehicle’s lights in reduced visibilities, but that is not always the case.

We also recommend what’s called the 3-second-plus following distance rule. Watch the vehicle in front of you. When that vehicle gets past an object such as a sign, pole, bridge, etc., then count off three seconds. You should not arrive at that spot sooner than your count to three. If you do, then you are following too close! Also, you must add one second for every hazard that exists. Hazards include but are not limited to heavy traffic, rain, snow, fog, driving into the sun, etc. In some cases you might have to allow six, seven seconds (or even more) to be safe because of existing hazards.

If you eliminate all distractions while driving, you might be able to see a hazardous situation in time to avoid it or reduce the severity of a crash.

We recommend when driving in dense fog, heavy rain or snow is to drive in the right lane of a two lane roadway going in the same direction. In the event that a vehicle is traveling the wrong way, chances are that they will be in your left lane as they approach and pass by you.

When visibility is reduced, slow down, increase your following distances, manually turn on your lights and eliminate all distractions.

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