Grey clustering assessment of level of service for urban expressway segments

With the rapid development of ITS (intelligent transportation systems) technology and its application on urban expressway, the concept of highway level of service has been changing. The traffic condition with high speed and large volume is considered as good service quality. Based on the re-understanding of the concept of level of service, this paper selects non-dimensional traffic pressure and non-dimensional density as performance measures which embody the new concept well. After separating level of service of expressway into four classes, establishing each grey class whitening function and determining the corresponding threshold value, the service levels of expressway segment then have been determined. The validation of field data collected on segments of the 2^nd, 3^rd, 4^th and 5^th Urban Ring Road of Beijing indicated that the methodology put forward in this paper was correct and feasible.