This paper deals with the problem of finding the optimal roadway segment configuration for road-based surveillance technologies to estimate route travel times accurately. This problem is inherently a space discretization problem regardless of which travel time estimation function is used. The ad-hoc solution to this problem is the equidistant segment configuration, such as every half-mile, every one-mile. It is shown in this paper that the space discretization problem can be expressed as the common clustering problem. The novelty of the proposed approach is the use of preliminary vehicle trajectory data to obtain statistically significant traffic regime at the study route. Clustering of sample space-time trajectory data is proposed as a viable methodology for solving the optimal roadway segment configuration problem.