Just like an oven, vehicles can heat up to deadly temperatures in a matter of minutes. This annually leads to lethal, but preventable, events.
During a warm day a car acts much like a greenhouse by trapping the sun's heat. This heat is absorbed and transferred evenly throughout the car very efficiently. Once temperatures rise, the glass acts like an insulator to keep the heat from escaping.
Simply cracking a window will not allow for safe temperatures. This still threatens anyone inside a vehicle, especially pets, children and the elderly.