Fog can leave the sky bright while hiding the road ahead. That is why automatic headlights and a familiar route may give false confidence. Decide whether the journey can wait; if you must go, check the lights and wipers while parked and keep a place to stop in mind.
Know which light does which job
Switch on low-beam headlights. They also illuminate the taillights on normal vehicle setups, so drivers behind can see you. Daytime running lights may leave the rear dark. High beams reflect from fog and can make the view worse. If your vehicle has front fog lamps, use them as the owner's manual and local traffic rules allow; they illuminate a nearby area but do not extend safe stopping distance. Rear fog lamps, where fitted, have separate controls and local rules, so learn their use in the manual because the symbols and permitted use are not interchangeable. The National Weather Service fog guidance recommends low beams, optional fog lights and no high beams.
Before leaving, confirm both low beams and rear lights work. Clean the windshield inside and out, mirrors and lamp lenses. Check that the wipers clear the glass without smearing and that the defogger works. Set navigation and climate controls before moving. Fog does not become safer because a lamp has been switched on; the light only helps you and others see what remains visible.
Test the rear fog-lamp control while parked if your car has one, and learn its dashboard indicator. A rear fog lamp is bright and can dazzle drivers behind in clear conditions, so use it only as the manual and local rules intend. Do not rely on automatic headlamps to decide every fog situation for you. Look at the actual lighting state before entering the road.
Give the windshield time to clear if cabin humidity is part of the problem. A clean outside pane cannot fix condensation inside. Use the vehicle's ventilation or defogging instructions and wait until the necessary glass is clear. If the defogger or wipers fail, reconsider the trip. Driving into fog with an already compromised view is unsafe.
Drive for the distance you can see
Reduce speed before entering a fog bank. Leave a larger gap than in clear weather and use the road markings as a reference when they are visible. Do not follow another car's taillights into a speed or position you cannot independently judge. Avoid abrupt lane changes or passing. The National Weather Service's dense fog rules say to be able to stop within the distance you can see.
Moisture can build on the glass even after it looked clear at home. If it does, use the vehicle's defogger and wipers according to the manual. If visibility becomes too short to read the road and traffic, plan a safe exit from the travel lane; do not try to solve the problem by turning on high beams or speeding up to escape the patch.
Use road markings only while you can see them well enough to understand the lane. Do not stare at the taillights of another car and follow it through an intersection or turn without your own view. Increase the gap so a sudden slowdown ahead does not force hard braking on a slick road. If visibility varies from one low spot to the next, set your pace for the worst patch you can reasonably anticipate.
Stop outside the traffic path
A parking lot, rest area or other place clear of moving traffic is preferable to a shoulder. Signal early, move slowly and stop fully out of the lane. In near-zero visibility, the Weather Service advises hazards while pulling into a safe place and, if no lot is available, pulling as far off the road as possible. Follow the applicable local rules for hazard lights; their use while a vehicle is moving differs by jurisdiction. A shoulder is a last resort, not a waiting lane. If you cannot safely reach an off-road place, reduce speed and maintain control while seeking one.
Once parked, keep the car out of the path of other drivers and follow local roadside guidance. Tell someone your location if you are delayed. Wait for visibility to improve, change the route or postpone travel. Do not rejoin traffic just because a few cars passed successfully; their visibility and stopping distance may differ from yours. If the only available pull-off is unsafe, contact local assistance for guidance and stay off the foggy roadway.
Before moving again, clear the glass and reassess the route ahead. A fog bank can return after a brief clear stretch. The decision to continue should be based on what you can see now and where you can stop next, not on the number of miles left.
