What factors can affect a vehicle's speed when measured?

Traffic conditions, road gradients, and weather conditions play a crucial role in how a vehicle's speed is measured and can significantly affect that speed.

Traffic conditions can include the density of vehicles on the road, which can either slow down or speed up a vehicle depending on whether the traffic is heavy or light. Road gradients, such as inclines or declines, can also influence speed; a vehicle moving uphill may slow down due to the increased effort required, whereas moving downhill could result in a faster speed due to gravity's assistance. Weather conditions, such as rain or snow, can create hazardous driving situations that compel drivers to adjust their speed for safety, ultimately affecting the measured speed of their vehicle.

In contrast, while vehicle design and engine type, driver experience, and vehicle age, as well as road signage and lighting conditions, might influence driving behavior, they do not directly impact the physical measurement of speed in the same way that traffic, gradients, and weather do. Therefore, the factors highlighted in the chosen answer provide a more direct connection to how speed can fluctuate under different roadway circumstances.