Name a situation where a radar device might produce false speed readings.

In the context of radar speed measurement, multiple vehicles closely spaced in the detection zone can complicate the readings because the radar device may struggle to isolate the speed of a single target. When several vehicles are near together, the radar signal can bounce off more than one vehicle simultaneously, causing interference with the signal's return and leading to inaccurate speed readings. The device may mistakenly calculate the speed of one vehicle while attributing it to another, or it could average out speeds from multiple targets, resulting in a false reading.

While other options may also lead to inaccuracies—such as environmental factors or device malfunctions—they do not directly address the principle of radar operation in detecting the speed of individual vehicles. The scenario of multiple vehicles challenges the fundamental way radar devices are designed to measure speed, making it a clear situation where false readings can occur.