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19
Macroscopic Relations of Urban Traffic Variables: An Analysis of Instability
, 2010
"... Recent experimental work has shown that the average flow and average density within certain urban networks are related by a unique, reproducible curve known as the Macroscopic Fundamental Diagram (MFD). For networks consisting of a single route this MFD can be predicted analytically; but when the ne ..."
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Cited by 25 (6 self)
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Recent experimental work has shown that the average flow and average density within certain urban networks are related by a unique, reproducible curve known as the Macroscopic Fundamental Diagram (MFD). For networks consisting of a single route this MFD can be predicted analytically; but when the networks consist of multiple overlapping routes experience shows that the flows observed in congestion for a given density are less than those one would predict if the routes were homogeneously congested and did not overlap. These types of networks also tend to jam at densities that are only a fraction of their routes ’ average jam density. This paper provides an explanation for this phenomena. It shows that, even for perfectly homogeneous networks with spatially uniform travel patterns, symmetric equilibrium patterns with equal flows and densities across all links are unstable if the average network density is sufficiently high. Instead, the stable equilibrium patterns are asymmetric. For this reason the networks jam at lower densities and exhibit lower flows than one would predict if traffic was evenly distributed. Analysis of small idealized networks that can be treated as simple dynamical systems shows that these networks undergo a bifurcation at a networkspecific critical density such that for lower
Clockwise Hysteresis Loops in the Macroscopic Fundamental Diagram
, 2010
"... A recent study reported that the Macroscopic Fundamental Diagram of a medium size city exhibited a clockwise hysteresis loop on a day in which a major disturbance caused many drivers to switch to unfamiliar routes. This paper shows that clockwise loops are to be expected when there are disturbances, ..."
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Cited by 12 (1 self)
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A recent study reported that the Macroscopic Fundamental Diagram of a medium size city exhibited a clockwise hysteresis loop on a day in which a major disturbance caused many drivers to switch to unfamiliar routes. This paper shows that clockwise loops are to be expected when there are disturbances, especially if the disturbances cause a significant fraction of the drivers to not change routes adaptively. It is shown that when drivers are not adaptive networks are inherently more unstable as they recover from congestion than as they are loaded. In other words, during recovery congestion tends more strongly toward unevenness because very congested areas clear more slowly than less congested areas. Since it is known that uneven congestion distributions reduce network flows, it follows that lower network flows should arise during recovery, resulting in clockwise loops. Fortunately, in sufficient numbers, drivers that choose routes adaptively to avoid congested areas help to even out congestion during recovery, increasing flow. Thus, clockwise loops are less likely to occur when driver adaptivity is high.
A comparative study of Macroscopic Fundamental Diagrams of arterial road networks . . .
, 2012
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SelfStabilizing Decentralized Signal Control of Realistic, Saturated Network Traffic
, 2010
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An AreaAggregated Dynamic Traffic Simulation Model
"... Microscopic and macroscopic dynamic traffic models not fast enough to run in an optimization loop to coordinate traffic measures over areas of twice a trip length (50x50 km). Moreover, in strategic planning there are models with a spatial high level of detail, but lacking the features of traffic dyn ..."
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Microscopic and macroscopic dynamic traffic models not fast enough to run in an optimization loop to coordinate traffic measures over areas of twice a trip length (50x50 km). Moreover, in strategic planning there are models with a spatial high level of detail, but lacking the features of traffic dynamics. This paper introduces the Network Transmission Model (NTM), a model based on areas, exploiting the Macroscopic or Network Fundamental Diagram (NFD). For the first time, a full operational model is proposed which can be implemented in a network divided into multiple subnetworks, and the physical properties of spillback of traffic jams for subnetwork to subnetwork is ensured. The proposed model calculates the traffic flow between to cell as the minimum of the demand in the origin cell and the supply in the destination cell. The demand first increasing and then decreasing as function of the accumulation in the cell; the supply is first constant and then decreasing as function of the accumulation. Moreover, demand over the boundaries of two cells is restricted by a capacity. This system ensures that traffic characteristics move forward in free flow, congestion moves backward and the NFD is conserved. Adding the capacity gives qualitatively reasonable effects of inhomogeneity. The model applied on a test case with multiple destinations, and rerouting and perimeter control are tested as control measures.
The Impact of Traffic Dynamics on the Macroscopic Fundamental Diagram
, 2012
"... Word count: nr of words in abstract 199 nr of words 5480 nr of figures & tables 8 * 250 = 2000 total 7480 ..."
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Word count: nr of words in abstract 199 nr of words 5480 nr of figures & tables 8 * 250 = 2000 total 7480
Empirics of a Generalized Macroscopic Fundamental Diagram
, 2012
"... Word count: nr of words in abstract 240 nr of words (including abstract) 4392 nr of figures & tables 12 * 250 = 3000 ..."
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Word count: nr of words in abstract 240 nr of words (including abstract) 4392 nr of figures & tables 12 * 250 = 3000
Keywords: Variational
, 2012
"... Macroscopic fundamental diagram macroscopic fundamental diagram (MFD). It has also been shown that heterogeneity in the At the link scale, traffic flows can be unpredictable or chaotic when a network is critically congested because of different driving behavior patterns, the effect of route choice, ..."
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Macroscopic fundamental diagram macroscopic fundamental diagram (MFD). It has also been shown that heterogeneity in the At the link scale, traffic flows can be unpredictable or chaotic when a network is critically congested because of different driving behavior patterns, the effect of route choice, the fast dynamics of link travel times and origin–destination tables and the computational complexity (too many particles/cars). These observations make the development of global traffic management strategies, to improve mobility for a large signalized traffic network with a microscopic analysis, intractable. An alternative is a hierarchical control structure, where a network can be partitioned in homogeneous regions (with small spatial
Optimal Hybrid Perimeter and Switching Plans Control for Urban Traffic Networks
 IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY
, 2014
"... Since centralized control of urban networks with detailed modeling approaches is computationally complex, developing efficient hierarchical control strategies based on aggregate modeling is of great importance. The dynamics of a heterogeneous largescale urban network is modeled as R homogeneous r ..."
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Since centralized control of urban networks with detailed modeling approaches is computationally complex, developing efficient hierarchical control strategies based on aggregate modeling is of great importance. The dynamics of a heterogeneous largescale urban network is modeled as R homogeneous regions with the macroscopic fundamental diagrams (MFDs) representation. The MFD provides for homogeneous network regions a unimodal, lowscatter relationship between network vehicle density and network spacemean flow. In this paper, the optimal hybrid control problem for an Rregion MFD network is formulated as a mixedinteger nonlinear optimization problem, where two types of controllers are introduced: 1) perimeter controllers and 2) switching signal timing plans controllers. The perimeter controllers are located on the border between the regions, as they manipulate the transfer flows between them, while the switching controllers influence the dynamics of the urban regions, as they define the shape of the MFDs and as a result affect the internal flows within each region. Moreover, to decrease the computational complexity due to the nonlinear and nonconvex nature of the optimization problem, we reformulate the problem as a mixedinteger linear programming (MILP) problem utilizing piecewise affine approximation techniques. Two different approaches for transformation of the original model and building up MILP problems are presented, and the performances of the approximated methods along with the original problem formulation are evaluated and compared for different traffic scenarios of a tworegion urban case study.
Transportation Research Part B
"... journal homepage: www.elsevier.com/locate/trb On the distribution of urban road space for multimodal ..."
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journal homepage: www.elsevier.com/locate/trb On the distribution of urban road space for multimodal