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The formula that represents Average Travel Speed is best illustrated by summing the product of frequency and speed, and then dividing that total by the frequency. This approach effectively calculates a weighted average, where each speed is considered in proportion to how often it occurs (the frequency).

In transportation and traffic studies, average speed is often evaluated based on how much distance is covered over a certain period of time. However, this formula accounts for the varying speeds that might be experienced over different segments or conditions, hence the importance of the frequency factor. It helps in representing a more accurate average speed as it reflects the influence of each distinct speed based on its occurrence.

This method contrasts with other choices that either misrepresent how to calculate average speed or do not integrate frequency effectively. For instance, simply summing speeds does not factor in how often each speed occurs, which can skew results, if, for example, some speeds are more common than others. Alternatively, summing distances divided by travel time is a direct calculation of average speed, but it does not incorporate variations based on frequency, making the choice that includes frequency the most precise representation of Average Travel Speed in a scenario with multiple speeds.