A hypothesis based on traffic pressure and its application on evaluating level of service for basic freeway segments

After the application of ITS (Intelligent Transportation Systems), a security travel at high volume and speed is hoped but a travel at low volume and high speed. Therefore the level of service is regarded as relative high when traffic flow operates safely under high volume and speed (also high density). This is just the target of ITS. The concept of service saturation or relative level of service is proposed to explain the above thinking in this paper. A traffic flow continuity hypothesis based on traffic pressure is brought forward. Analogy relationship between traffic flow and fluid flow is adjusted. Contrasting fluid mechanics and traffic flow, the concept of traffic pressure under steady traffic flow is defined. The concept of relative traffic pressure P~ is interesting. There is always P~≤1 under any traffic condition (it may be negative or positive). Based on continuum equation set up, viscosity momentum differential equation is given. The feasibility of evaluating level of service (LOS) of highway by non-dimensional traffic pressure is analyzed and field data collected by using traffic detectors on Guangzhou-Foshan freeway in south of China are used to verify the hypothesis proposed in this paper. It is concluded that the observed data show that non-dimensional traffic pressure could be used to evaluate LOS.