The common belief that a car’s rubber tires protect occupants from a lightning strike is a widespread misconception. The tires are ultimately irrelevant to safety when a bolt of lightning, which has traveled miles through insulating air, is involved. Most modern hard-topped vehicles with a full metal chassis are a safe place to be during a thunderstorm. This protection does not come from insulation but from the vehicle’s metallic structure, which redirects the massive electrical charge around the passenger compartment.
The Faraday Cage Principle
The protection offered by a metal-bodied car is due to the Faraday Cage effect, named after the scientist Michael Faraday who discovered it in 1836. A Faraday Cage is a conductive enclosure that shields its contents from external static and electromagnetic fields. When an electric charge, such as a lightning bolt, contacts the exterior of this conductive shell, the charge immediately redistributes itself.
The free electrons within the car’s metal body move rapidly in response to the external electric field created by the lightning. This movement causes the charges to reside entirely on the outer surface of the conductor, effectively canceling out the electric field within the enclosed space. Because the net electric field inside the vehicle becomes zero, the occupants remain safe from the electrical current. The car’s metal frame acts as a shield by shunting the charge across its surface and away from the interior.
The Path of the Electrical Current
When a vehicle is struck by lightning, the bolt often contacts the highest point, such as the radio antenna or the roofline. The lightning current, which can reach tens of thousands of amperes, follows the path of least resistance across the vehicle’s outer metal shell. This phenomenon is known as the “skin effect,” where high-frequency electrical currents travel mostly along the outer surface of a conductor.
The current seeks a path to the ground to complete the electrical circuit. It typically exits through the tires, which are poor conductors, forcing the discharge to jump to the road. While occupants are protected inside the Faraday Cage, the vehicle often sustains damage. The intense heat from the strike can partially melt the antenna or cause the rear window’s defrosting wires to shatter the glass. A portion of the electrical discharge may induce high-voltage currents in the car’s wiring, potentially destroying sensitive electronic components and leaving the vehicle inoperable.
Internal Safety Measures During a Storm
While the metal shell protects occupants from the external charge, the electrical current can still find a path into the cabin if interior objects are touched. You should pull over to the side of the road in a safe location and turn off the engine. Keep the windows completely rolled up to maintain the integrity of the enclosure.
Occupants must avoid touching any metal components connected to the car’s exterior, such as door handles, the steering wheel, or the radio. Touching these items can create a secondary pathway for the current to travel through the body if the charge arcs inside. You should also refrain from using plugged-in electronics or charging cords, as lightning can cause electrical surges in the car’s system. The safest position is to sit with your hands in your lap, waiting out the storm until at least 30 minutes after the last clap of thunder.
Vehicles That Offer Less Protection
The protection afforded by the Faraday Cage depends on the continuity and conductivity of the vehicle’s exterior shell. Vehicles that lack a continuous, conductive metal body do not offer the same safety from a lightning strike. This includes convertibles, even if the cloth or soft top is fully deployed, because a fabric top is non-conductive and cannot channel the electrical current away from the passengers.
Vehicles constructed primarily of non-metallic materials, such as fiberglass or carbon fiber, do not effectively create a Faraday Cage. Since these materials are poor conductors, the lightning current will not be confined to the exterior surface and may arc through the interior, posing a direct threat to occupants. Open vehicles, like motorcycles, golf carts, and tractors, provide virtually no protection because they lack the conductive body necessary to shield the person inside. In these situations, the occupant becomes the most likely path for the lightning to travel to the ground.