Operating speed: review and recommendations for future research

The primary aim of transportation is to facilitate movement of people and goods in a safe and efficient manner. To meet the objectives of transportation, there are many challenges from an engineering perspective. Among them, geometric design is the foremost requisite in planning and functional design of a roadway system. In this context, operating speed plays a key role for controlling geometric design criteria and securing safe operational control. The operating speed varies according to locations and roadway characteristics if previous studies were anything to go by. It is found to be sensitive with regard to roadway types, terrain types, geometric design elements such as horizontal and vertical curves, and their combinations. In past studies, operating speed was observed to vary based on traffic control type and operational conditions. Many studies have determined operating speed for passenger cars and suggested models for evaluating traffic operational performance while showing inconsistency in geometric design. The present study provides a very comprehensive review of literature on the operating speed estimated under different roadway, geometric and traffic conditions across the nations. It is found that the operating speed studies performed under homogeneous and heterogeneous traffic conditions on multilane highways are limited and do not provide generalized solutions in terms of both safety and efficiency aspects. Thus, this study looks at operating speed and determining it by involving various geometric and roadway conditions and considering significant variables, data acquisition methods and equipment used and models for prediction. It highlights the need for future studies on operating speed characteristics, which is one of the major performance measures for evaluating roadway geometry consistency and traffic control performance.