Modelling Signalised Intersections Reliability of Functioning

Abstract

The article addresses a fundamental aspect of traffic, i.e. the operation of traffic signals at intersections, in reference to the reliability theory. In many cases, when intersections carry substantial amounts of traffic, selecting control parameters to produce satisfactory traffic conditions is quite difficult. Design methods do not cover all possible situations which are the result of intersection geometry and location within the city. Neither do they account for reduced capacity in bad weather. Inefficient signal-controlled intersections have a strong influence on motorists, causing frustration and fatigue and eventually leading to risky behaviour in road traffic. Sustained congestion in urban areas has a negative effect on the residents and how they function in the urban environment. As a consequence, big city dwellers who drive grow accustomed to poor traffic conditions and are ready to accept some time lost at peak times. When designing traffic signals, the methods should relate to the size of the city and levels of traffic overload that are acceptable to motorists, rather than identify inferior levels of free flow only. This particular field of study is suited for the reliability theory as presented in the article. When analysing the reliability of groups of traffic lanes, we must be clear about boundary traffic conditions where the reliability state transitions into the unreliability state. The state of reliability is when an intersection operates seamlessly and traffic volume Q is below capacity C (periods in between peak times or at night-time). The article will show the division of the reliability state into levels. This helps to define the boundaries based on boundary values of selected measures of those traffic conditions that are of particular importance to us when managing junction traffic. Once these values are identified and geometry and weather factors are included, traffic signals can be designed more efficiently and urban traffic will improve as a result.