Final answer:
In a scenario where a vehicle is submerged in water, it is vital to open the windows and doors to escape as quickly as possible and to call for help immediately if feasible. Waiting inside the vehicle is not safe. Drowning situations require urgent and calm action, with escape being the top priority.
Step-by-step explanation:
When your vehicle goes off the road and lands in deep water beginning to sink and becomes mostly submerged, the best course of action to ensure safety is to open the windows and doors to escape. This is critical because the water pressure may make it impossible to open the doors once the water gets too high, and the electrical system may fail, rendering automatic windows non-operational. In such situations, staying calm is imperative, but waiting for help while the car sinks further puts the occupants at greater risk. It is also useful to call for help immediately if it is possible to do so without delaying your escape.
The reality of a drowning situation highlights the importance of quick and calm action. Due to the muscular spasm that seals the airway, shouting for help is often not possible, which contradicts the myth that a drowning person will call out and wave for attention. Instead, they are more likely to display instinctive, subtle signs such as having their head low in the water with uncontrolled movements of arms and legs. Thus, escaping the vehicle as quickly as possible is crucial, just as removing a person from water is the first step before starting CPR once they are on stable ground.