What is the total number of headlights that can be illuminated on the sides of a vehicle at one time?

The total number of headlights that can be illuminated on the sides of a vehicle at one time is two. Typically, vehicles are equipped with two headlights at the front, used to illuminate the roadway ahead. These headlights can be operated simultaneously, providing the necessary visibility for the driver.

It's worth noting that while some vehicles have additional lighting features, such as fog lights or marker lights, these do not contribute to the count of headlights illuminating the sides of the vehicle in a standard configuration. The focus of this question is on the function of primary headlights, which are designed to enhance visibility during nighttime and adverse weather conditions. Thus, the correct answer about the illumination capacity of headlights on the sides is two.