What might interfere with the ability to accurately read a vehicle's speed with radar?

Accurately reading a vehicle's speed with radar can indeed be compromised by vehicles approaching at sharp angles or changes in road gradient. When a vehicle travels toward the radar unit at a significant angle, the radar might not receive the reflected signal effectively, which can lead to inaccurate speed readings due to the geometry of the radar wave's interaction with the vehicle. Similarly, if there is a sudden change in road gradient, the radar may misinterpret the vehicle's speed due to variable distances between the radar and the vehicle, or alterations in the Doppler shift created by the incline or decline. This geometric and environmental interaction is crucial for maintaining the reliability of speed readings in radar operations.

The other options, while they may present challenges, do not primarily influence the radar's ability to measure speed in the same manner. For instance, low visibility due to weather conditions could affect a law enforcement officer's ability to visually identify vehicles but does not technically interfere with the radar's measurement capabilities. The distance of the vehicle from the radar can affect accuracy; however, most radar systems are designed to account for and measure speeds at various distances effectively, as long as the conditions are appropriate. Alternative traffic signs nearby may create potential distractions but do not directly influence the radar's measurement function.