Final answer:
To safely start an automatic transmission car, it should be in Park (P) or Neutral (N) gear to prevent unexpected movement. Park is generally required and a safety feature enforced by a shift interlock system that might also allow starting in Neutral under certain circumstances.
Step-by-step explanation:
When starting a car with an automatic transmission, it should be in Park (P) or Neutral (N) gear. These positions ensure that the vehicle does not move unexpectedly when the engine is started, which could lead to unsafe situations. In addition to safety, it's often a mechanical requirement of the vehicle that it must be in Park or Neutral to start.
Many cars with automatic transmissions will not allow the key to turn in the ignition unless the gear is in Park. This is a safety feature called a shift interlock that prevents accidental movement of the vehicle. If for some reason the vehicle does not start in Park due to an issue with the interlock system or otherwise, Neutral provides an alternative that still ensures the vehicle remains stationary during starting.