THE AVERAGE VEHICLE SPEED IN A DENSE TRAFFIC FLOW WITH THREE SLOW-MOVING VEHICLES ON A ROAD SECTION WITH LIMITED MANOEUVRING OPPORTUNITIES

Abstract

Forecasting the urban traffic flow parameters remains one of the most challenging tasks for scientists and practitioners around the globe. The fundamental diagram of a traffic flow, which is a statistically established relationship between flow parameters, helps to solve this task. This diagram shows a decrease in speed with an increase in flow density, and one of the explanations for this is that drivers are forced to adapt to the speed of slower vehicles in front. This affects the variation of speed and indicates that it is reasonable to consider it a random variable with the mean and distribution, which depend on traffic conditions. For free flow, the normal vehicle speed distribution is generally recognised, while the issue of what distribution to use to represent the speed in dense traffic remains open. The current research contributes to the clarification of this issue, and its core is an elaboration of the process of forming an average speed of similar vehicles in the densest traffic flow on a road section with no overtaking opportunities. The search for this average value was started by considering the simplest situations of a vehicle platoon, where all vehicles are expected to move at the same maximum permitted speed except for one or two slow-moving vehicles that limit the speed of the others. This paper is a logical extension of these situations and is devoted to deriving a formula to calculate the average speed of a traffic flow with three slow-moving vehicles. A generalisation of the obtained results will create a sound basis for deriving a formula to calculate the average speed of a dense traffic flow with any number of slow-moving vehicles. The availability of this formula can be a starting point for understanding the changes in normally distributed free-flow speed caused by a dense traffic flow.

Keywords: traffic speed, average speed, traffic flow, flow density, traffic lane, traffic conditions, analytical modelling, transport system.