Fog does more than shorten the distance you can see. It distorts the visual cues drivers depend on to judge speed and closing distance, which is why even experienced motorists misjudge how quickly they are approaching the vehicle ahead. Objects viewed through fog appear farther away and slower moving than they actually are. By the time a shape resolves into something recognizable, the margin available for a controlled response is smaller than instinct suggests.
Reduce Speed Before Visibility Forces You To
Your safe speed in fog is governed by a single question: can you stop within the distance you can actually see? Posted limits assume clear conditions and offer no protection once visibility collapses. Slow down early and gradually. Braking hard after you have already entered a dense bank invites a collision from behind, because the driver following you is working with the same degraded information you are.
Use Low Beams, Never High Beams
High beams are counterproductive in fog. The light strikes suspended water droplets and scatters back toward the windshield, producing glare that reduces what you can see rather than improving it. Low beams direct light downward onto the road surface where it remains useful. Dedicated fog lights, if your vehicle has them, are mounted low for the same reason.
Buy Yourself Room, and Keep the Glass Clear
Extend your following distance well past the interval you would normally accept. You need time to react to a hazard that emerges from a grey wall with almost no warning. Run the defroster and air conditioning together, since fog raises humidity and interior condensation forms faster than most drivers expect. Exterior grime matters as well, because a dirty windshield scatters oncoming light and compounds the glare.
Steer by the painted edge line on your right rather than the center line. Drivers tend to drift toward whatever reference they are watching, and the center line leads toward oncoming traffic.
Know When to Stop Driving
If conditions deteriorate to the point where you cannot maintain a safe speed, leave the roadway entirely. Avoid stopping in a travel lane or on the shoulder, because approaching drivers steer toward tail lights on the assumption that they are moving. Take an exit or pull into a parking area, then switch off your lights and set the parking brake. Leaving your lights on invites another driver to follow you off the road.
Requirements for headlight use in reduced visibility vary between states. Check the rules that apply where you drive before you need them.