Speed D Link
bar over vt= bar over vs +
where σ 2 over s is the variance of the instantaneous speed observations. Obviously, if all the vehicles in the traffic stream are traveling with the same speed (i.e., σ 2 over s = 0) the two speed estimates are equal. Therefore, in conditions under which vehicles are expected to be moving with similar speds, i.e., in uncongested conditions the difference between the two means will be very small, while in stop and go operations in congested conditions this difference will be significant.