When two vehicles are traveling in the same direction, the Doppler shift produced is:

When two vehicles are traveling in the same direction, the Doppler shift produced is smaller. This phenomenon occurs because the frequency of the wave emitted from the radar or lidar system is affected by the relative velocity between the source and the observer.

In the case of two vehicles moving in identical directions, the speed at which they approach or separate from each other reduces the relative speed. Consequently, the change in frequency, which is the basis of the Doppler shift, becomes less pronounced than it would be if the vehicles were moving towards or away from each other at different speeds.

As the vehicles maintain similar velocities in the same direction, the resulting frequency change becomes minimal, leading to a smaller Doppler shift. This concept is crucial in understanding how radar and lidar systems measure speed; the relationship between the movement of the source and the observer directly influences the accuracy and interpretation of the data gathered.