01557549

Component

Recurring bottleneck sections are the direct cause of congestion in urban expressways. Off-ramp bottlenecks can generate more adverse impact to mainline flow. However, few studies focus on off-ramp bottlenecks. In this paper, three off-ramp bottlenecks are analyzed using data collected from multiple days. The main findings are: (1) Different kinds of relationship between Pre-queue flow (PQF) and queue discharge flow (QDF) are found with different diverge-ratios. The transformed cumulative curves are used to analyze the cause of the flow features. (2) Breakdown is firstly triggered at the lane or lane group with highest occupancy during the transition process from free flow to congestion flow. (3) As soon as the occupancy of the initial congested lane or lane group rises to near 30%, the congestion begins to spread laterally to the rest lanes. (4) Different congestion propagation modes in longitudinal direction are found: Congestion travels upstream in one-pipe at bottlenecks with high diverge-ratios while propagations are alternative lateral and longitudinal at bottlenecks with low diverge-ratios. (5) The transition from congestion flow to free flow is the inverse process of that from free flow to congestion flow. These findings provide a detailed description of traffic flow phase transition that can be considered as a useful reference to theoretical studies and help engineers optimizing traffic management schemes.

This paper was sponsored by TRB committee AHB45 Traffic Flow Theory and Characteristics.

01550057

15-2681

English

18p

2015

Transportation Research Board 94th Annual Meeting

Digital/other

Figures; References; Tables

Bottlenecks; Diverging traffic; Expressways; Off ramps; Traffic congestion; Traffic flow

Shanghai (China)

Highways; Operations and Traffic Management; Planning and Forecasting; I71: Traffic Theory

Transportation Research Board Annual Meeting 2015 Paper #15-2681

TRIS, TRB, ATRI

Dec 30 2014 12:55PM