What error is caused when the radar beam is angled across the roadway rather than pointing straight down the roadway?

The correct answer focuses on the concept of "cosine error." This type of error occurs when the radar beam is not perfectly aligned with the direction of the target's motion, causing the measured speed to be less than the actual speed of the vehicle.

In essence, when the radar beam is angled across the roadway, the component of the vehicle's speed that is being measured decreases due to the angle. This is a direct result of the geometry involved in how speed is calculated. The radar device effectively measures a component of the true speed; therefore, the greater the angle from the direction of travel, the larger the error introduced in the speed reading.

The cosine function plays a key role here, as it relates the angles to the ratio of the adjacent side over the hypotenuse in a right triangle. If the radar is not aimed directly at the oncoming vehicle (which represents a 0-degree angle), the measurement only captures a fraction of the actual speed, leading to the cosine error being calculated as the actual speed multiplied by the cosine of the angle. As a consequence, this results in an underestimation of the vehicle's speed.

Understanding this concept is crucial for anyone using radar technology in speed detection, as it highlights the importance of