No abstract

Merge junctions are the key elements in the freeway system, as they are likely to function as bottlenecks. Investigations into breakdown occurrence at ramp junctions have demonstrated that when the groups of several vehicles following each other enter the freeway from the ramp, they are expected to create 'turbulence' resulting from lane changes, decelerations of vehicles on the mainline and inevitably by the cars merging from the on-ramp. This turbulence can lead to breakdown when the level of mainline demand is adequately high. In other words, the impact of a ramp vehicle on capacity is higher than that of a mainline vehicle, which indicates that a part of vehicles will simultaneously occupy two lanes during the process of changing them thus momentarily decreasing the capacity of the link. This feature becomes particularly important near bottlenecks where it might reduce the already limited throughput. The article introduces the main approaches, methodology, principles and stages of transport demand management on freeways that are aimed at improving the operation quality of transport facilities, including road safety. The technique allows evaluating and optimizing a Ramp-Metering (RM) concept from the viewpoint of minimizing the length of queues on ramps and a possibility of transport congestion. The proposed algorithm estimates the probability of starting congestion formation on the ramp using objective information on traffic conditions in each segment of the highway, which is based on the criterion for vehicle density on the lane. The last chapter shows the examples of traffic flow optimization on Western bypass ramps in Vilnius comparing two strategies for access control management using one or several vehicles per lane. Conclusions, trends and work on future investigations are presented at the end of the article.

The paper discusses problems of assessing the impact of mass attraction centers on the adjacent street and road network in the process of their functioning, expansion or conversion. The choice of criteria for assessing the organization of traffic flow, given in the Russian and foreign literature, has been substantiated, in particular, it is proposed to use v/c ratio for adjacent junction and corresponding level of traffic service (LOS). The main models for estimating capacity of signalized intersections are presented. The procedures of forming a mathematical model for estimating the load factor of signalized intersections is shown. The concepts of lane group capacity, total lost time per cycle, phase coefficients, saturation flow rate, and coefficients taking into account the decrease in the ideal saturation flow rate are explained. A mathematical model for estimating transport demand is presented, which allows to calculate the intensity of traffic flow to and from the center of mass attraction on the basis of the total traffic flow of correspondence, share of visitors in individual transport, average filling of individual transport, and coefficient of daily irregularity upon arrival and departure of visitors on an individual transport. An integrated mathematical model of loaf factor is proposed which includes parameters for estimating transport demand for centers of mass embarrassment and parameters that determine the signalized intersections capacity. The uniqueness of the integrated model is that it simultaneously involves parameters reflecting the demand and capacity of loading intersection. Recommendations are made on assessing the level of traffic service flows and the v/s ratio, based on the data of transport demand and capacity, adjacent to the centers of mass attraction of the road network. The presented method of estimating the LOS based on the capacity of the signalized intersections allows us to estimate the influence degree of mass attraction centers on the adjacent urban road network.