Assessment of Level of Service on urban roads: a revisit to past studies

Level of Service (LOS) of a road describes the quality of service that a roadway facility is providing to its users. It often becomes necessary to determine LOS to assess the present performance of the road and to improve it, if required. Although several measures of effectiveness (MOEs) are available in the literature, it is necessary to choose the appropriate MOE that is the best suitable to the local traffic condition of that region. This article provides a state-of-the-art literature review on various LOS criteria proposed by researchers based on different MOEs on urban roads. After a comprehensive search using the relevant keywords, a total of 93 research papers published in journals and conference proceedings indexed in Scopus, Science Citation, Google Scholar and Web of Science were primarily identified. However, after two-phased screenings, 52 research papers were shortlisted and reviewed in this study. The MOEs presented in these papers include some conventional parameters such as ‘speed’, ‘travel time’, ‘density’, etc. as well as some unconventional ones like ‘Congestion Index’ (CI), ‘Coefficient of Variation of Speed’ (CVS), ‘Acceleration Noise’ (AN), ‘Buffer Time Index’ (BTI), ‘Planning Time Index’ (PTI), etc. This study summarizes the contribution of previous research efforts toward the knowledge of LOS on urban roads and presents a comparison among the LOS criteria proposed in past studies. The results indicated that there is wide inconsistency in the outcome of speed-based LOS thresholds suggested in different studies. This is probably due to either the change in vehicle characteristics and driving culture across countries or the selection of different clustering approaches. After reviewing the previous studies, it was realized that a maximum of three to four classes are enough to represent LOS based on the users’ perception as the users cannot differentiate among more than four classes. Moreover, MOEs based on travel time reliability can be adopted for measuring the service quality from a reliability perspective. The present paper highlights the advantages and disadvantages associated with different MOEs so that the reader can adapt the most suitable one compatible with the local traffic conditions and other circumstances. Also, the use of multiple MOEs can enhance the outcome if a single MOE lacks a better representation of LOS.