Abstract:
Because of dependence among travel time observations on signalized arterials, the estimation of variances of key statistics is not straightforward. The variance of the estimate of expected (mean) travel times obtained from n probe vehicles for the same link over a fixed time period may be shown to be of the form a+ b/n where a and bare link-specific parameters. Using data from a set of arterials, it is shown that a is positive for well traveled signalized links. This implies that the variance of the estimate does not go to zero with increasing n. Consequences of this fact for probe-based system are explored. While the results presented are for a specific set of links, we argue that because of the nature of the underlying travel time process, the broad conclusions would hold for most links with signal control.
tr54.pdf