Final answer:
When you approach an emergency vehicle assisting a vehicle, you should slow down and move over a lane safely, adhering to the 'Move Over' laws where applicable.
Step-by-step explanation:
When approaching an emergency vehicle that is assisting a vehicle on the side of the road, the correct protocol is not explicitly stated among the provided options of stopping, running toward, or alongside the ambulance. In usual circumstances, it is essential to slow down and, if possible, move over to provide a safe distance for emergency responders, often referred to as the 'Move Over' law in many regions. This law typically requires drivers to move over a lane if they can do so safely, or to slow down significantly if moving over is not possible.
The Doppler shift effect mentioned can indeed help drivers recognize the approach and receding of an ambulance siren, which can be critical in deciding when to yield to the emergency vehicle. The information is not directly related to the action to be taken but helps in awareness of the emergency vehicle's location relative to the driver. Additionally, the perspective of motion can change depending on the observer's position, as in the examples with the bus passenger and sidewalk observer. However, this concept is more about physics than what action should be taken when near an emergency vehicle.