How does the chassis neutralize the excess of electrons from a lightning strike?
Tests** have shown safe results with an occupant inside a car exposed to a 1 million volt discharge but there will be exceptional situations. (e.g. open sunroof and with roof antenna.)
Those tests**, which you may search on Youtube, were even performed on a dry car. A wet car makes it easier for the >1kV/m E field stress as water is 80x stronger as a capacitor to conduct the charge to ground. It is minute contaminants in the medium that cause the arc to bifurcate and change direction slightly or "fork" in the general direction of opposite polarity.
How does the chassis ground on an automobile protect against lightning and how does the chassis neutralize the excess of electrons from a lightning strike?
Specifically what the chassis is doing is providing a low impedance path for current to travel around you rather than through you. Because the chassis is a cage arrangement of metal fully surrounding the passengers, it qualifies as a Faraday Cage, which is a device generally used to protect people or areas from electricity and or electromagnetic radiation. Because the chassis is also insulated from ground by the rubber of the tires and air beneath the car, it could also be considered to be protecting you, not only by being a better path for current than you, but also by being a potentially less good path than other nearby objects which might be taller or overall better conductors, like posts, wet trees, buildings, towers, lightning rods, larger vehicles.
Note that during a lightning strike, the electricity is not the only danger. There is also heat, fire, flash, flashburn, and potential explosion to consider, so being in a car when it is hit by lightning could still really suck and or be destructive or lethal.