Which of the following factors can interfere with radar signals?

Heavy traffic can interfere with radar signals primarily due to the multitude of vehicles present, which can create confusion in the radar's ability to accurately detect the speed of individual vehicles. When many vehicles are moving in close proximity, the radar may struggle to determine which signal to focus on, potentially leading to inaccurate speed readings or false signals. The overwhelming number of reflective surfaces and the complexity of the movement can cause the radar system to pick up multiple speeds rather than isolating a single target.

In contrast, clear weather typically provides optimal conditions for radar operation, as there are fewer environmental factors (like rain, fog, or snow) that can distort or absorb the radar signals. Vehicle size can impact the radar's return signal strength but doesn’t generally cause significant interference. Road conditions may affect overall traffic patterns or safety, but they do not inherently interfere with the functioning of radar signals in the same direct way that heavy traffic can.