Abstract
This paper proposes a model for estimating capacity of on-ramp merging section of urban expressway based on dynamics and gap acceptance theory, considering lane-changing processes and time headway loss. Survey data were collected from on-ramp merging sections of shanghai urban expressway system and showed that capacity drop of on-ramp merging section is caused by drivers’ lane-changing which may lead to unsteady speed of vehicles and so prolonged time headway compared to the minimum time headway corresponding to the maximum capacity. Three parameters (optimal time headway, time headway loss, and interference quantity of lane-changing) are given and a methodology by accumulating time headway loss due to lane-changing is developed to estimate the capacity drop. Results’ comparisons between real data and microsimulation of on-ramp merging sections and sensitivity analysis show that the proposed model can produce reliable and accurate results. This study also reveals that ramp flow and the difference between the optimal speed and the lane-changing speed of fleet have a great impact on capacity drop. This study is beneficial to evaluate congestion levels, to understand complex traffic phenomena, and so to find efficient solutions.
Highlights
Traffic congestion causes a huge disadvantage, such as waste of time and fuel as well as pollution
On-ramp merging sections usually become the bottleneck of urban expressway because headway cannot keep an optimal value; namely, the time headway is prolonged due to unsteady traffic flow caused by lane-changing of vehicles
In order to embody the relation between on-ramp flow and the flow of mainline lateral lane, this paper compares these data including VISSIM microsimulation and the model calculation results based on four kinds value of Vc, because there is not any road but only one lane in reality
Summary
Traffic congestion causes a huge disadvantage, such as waste of time and fuel as well as pollution. Congestion is usually induced by various kinds of bottleneck, among which the on-ramp merging section is an important position and has been widely studied. To enhance the capacity of an expressway with an on-ramp merging section, various kinds of methods have been proposed, in which an accurate traffic model that can efficiently estimate the capacity of on-ramp is most important while evaluating congestion levels, understanding complicated traffic phenomena, putting forward reasonable design scheme of infrastructure, and developing efficient operation strategies. Lertworawanich and Elefteriadou developed a new gap acceptance model through definition expressway capacity as function of ruin probability [9]. The overall objective of this study is to develop a new onramp merging section capacity estimation model of urban expressway, which considers lane-changing processes, vehicle speed of on-ramp, vehicle flow, and time headway distribution. The data obtained from the capacity model are compared with field-observed capacities and microsimulation result, and sensitivity analyses show that our model is robust; the implications of the research results are discussed in different fields
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