Which of the following is true regarding time-mean speed and space-mean speed?

The correct choice highlights an important aspect of traffic speed calculations. Time-mean speed refers to the average speed of vehicles measured over a certain time interval, which is obtained by averaging individual speeds of all vehicles that pass a point during a specific time period. Space-mean speed, on the other hand, is the average speed of vehicles measured over a specific distance, calculated by averaging the speeds of vehicles that travel that distance.

In typical traffic conditions, especially with factors like congestion or varying vehicle speeds, the time-mean speed will often be less than the space-mean speed. This occurs because time-mean speed gives more weight to the speeds of vehicles that spend longer at a given point (potentially slow-moving vehicles), while space-mean speed accounts for the time taken to cover a specific distance, which can be higher due to faster-moving vehicles completing the same distance more quickly.

The other options do not accurately represent their relationship. Space-mean speed being less than time-mean speed does not generally hold true in real-world conditions where variability and congestion are common. Additionally, it's incorrect to state that both means are identical, as they reflect different measurements and are affected by different factors. Lastly, time-mean speed and space-mean speed are comparable