What factor is key to consider when selecting a speed in rainy weather?

When driving in rainy weather, traction is the most critical factor to consider when selecting a speed. Rain creates a slick surface on the road, which can significantly reduce the tire's grip on the pavement. When the tires cannot maintain adequate traction, the risk of hydroplaning increases, where the vehicle rides on a layer of water instead of the road.

Choosing a slower speed allows for better control and increases the likelihood that tires will maintain contact with the road surface, enabling the driver to safely navigate turns, stop, and react to hazards. While visibility, engine power, and traffic density are important factors in driving conditions, they do not have the same direct impact on the control of the vehicle in slick, rainy conditions as traction does. A vehicle's speed should be adjusted primarily based on the traction available, ensuring that it remains safe and manageable despite adverse weather conditions.