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The relationship between time mean speed and space mean speed that was derived by Wardrop and presented in several textbooks is suitable for estimating time mean speeds from space mean speeds. In most cases, however, estimating space mean speed from time mean speed measurements is desired. Consequently, a new formulation utilizes the variance about the time mean speed as opposed to the variance about the space mean speed for the estimation of space mean speeds. It is demonstrated that space mean speeds are estimated within a margin of error from 0% to 1%. Furthermore, a relationship is developed between the space and time mean speed variances and between the space mean speed and the spatial travel time variance.
Rakha et al. (Sat,) studied this question.