Traffic Theory

An Analytical Approximation for the Macroscopic Fundamental Diagram of Urban Traffic

Daganzo, Carlos F.
Geroliminis, Nikolas
2008

This paper shows that a macroscopic fundamental diagram (MFD) relating average flow and average density must exist on any street with blocks of diverse widths and lengths, but no turns, even if all or some of the intersections are controlled by arbitrarily timed traffic signals. The timing patterns are assumed to be fixed in time. Exact analytical expressions in terms of a shortest path recipe are given, both, for the street’s capacity and its MFD. Approximate formulas that require little data are also given. For networks, the paper derives an upper bound for average flow conditional on...

Multimodal Transport Modeling for Nairobi, Kenya: Insights and Recommendations with an Evidence-Based Model

Gonzales, Eric J.
Chavis, Celeste
Li, Yuwei
Daganzo, Carlos F.
2009

Traffic congestion is a growing problem in Nairobi, Kenya, resulting from rapidly increasing population and the crowding of motorized traffic onto a limited street network. This report includes analysis of the traffic conditions in Nairobi, the expected effects of further growth in demand, and a set of recommendations for how to improve the performance of the street network. Data describing motorized vehicle traffic was used to build a simulation model of Nairobi’s street network considering cars and matatus. This model was used to analyze traffic conditions at the city-scale under...

Multimodal Traffic at Isolated Signalized Intersections: New Management Strategies to Increase Capacity

Xuan, Yiguang
Gayah, Vikash
Daganzo, Carlos
Cassidy, Michael
2009

New ideas are explored for managing multimodal traffic on isolated approaches to signalized intersections. Strategies are proposed that both: segregate distinct modes along the approach, and more effectively resolve the disruptive capacity-reducing conflicts that arise between through moving and turning traffic traveling in adjacent lanes. The proposed schemes produce capacities that consistently and significantly exceed those of conventional intersection treatments, and reduce travel delays for all modes. Observations at a real intersection support these claims.

Multimodal Traffic at Isolated Signalized Intersections: New Management Strategies and a Framework for Analysis

Xuan, Yiguang
Gayah, Vikash
Daganzo, Carlos F.
Cassidy, Michael J.
2010

New ideas are explored for managing multimodal traffic on isolated approaches to signalized intersections. Strategies are proposed that both: segregate distinct modes along the approach, and more effectively resolve the disruptive capacity-reducing conflicts that arise between through-moving and turning traffic traveling in adjacent lanes. The various schemes for doing this are systematically enumerated, using as a building block the simple case of an intersection approach on which two movements are in conflict; and a framework is formulated for estimating the capacities that these...

Macroscopic Relations of Urban Traffic Variables: An Analysis of Instability

Daganzo, Carlos F.
Gayah, Vikash V.
Gonzales, Eric J.
2010

For networks consisting of a single route the Macroscopic Fundamental Diagram (MFD) can be predicted analytically; but when the networks consist of multiple overlapping routes 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...

Exploring the Effect of Turning Maneuvers and Route Choice ona Simple Network

Gayah, Vikash V.
Daganzo, Carlos F.
2010

A simple symmetric network consisting of two tangent rings on which vehicles obey the Kinematic Wave Theory of traffic flow and can switch rings at the point of tangency is studied. An online adaptive simulation reveals that if there is any turning whatsoever the two-ring system becomes unevenly loaded for densities greater than the optimal density. This reduces flow. Furthermore, the two-ring system jams at significantly lower densities than the maximum density possible.

Clockwise Hysteresis Loops in the MacroscopicFundamental Diagram

Gayah, Vikash V.
Daganzo, Carlos F.
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, 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...

Macroscopic Fundamental Diagrams for Freeway Networks: Theory and Observation

Cassidy, Michael J.
Jang, Kitae
Daganzo, Carlos F.
2011

Macroscopic fundamental diagrams (MFDs), which relate the total time spent to the total distance traveled, are explored for freeway networks. It is proposed that these macrolevel relations should be observed if the data come from periods when all lanes on all links throughout the network are in either the congested or the uncongested regime. The theory pertains to freeway networks of any size, even when they are inhomogeneously congested and the data are variable in time. Analysis of vehicle trajectories from two freeway stretches of modest physical length supports this theory. Study...

Macroscopic Relations of Urban Traffic Variables: Bifurcations, Multivaluedness and Instability

Daganzo, Carlos F.
Gayah, Vikash V.
Gonzales, Eric J.
2011

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...

On the Macroscopic Stability of Freeway Traffic

Daganzo, Carlos F.
2011

A simple model of traffic flow is used to analyze the spatio-temporal distribution of flow and density on closed-loop homogeneous freeways with many ramps, which produce inflows and allow outflows. As we would expect, if the on-ramp demand is space-independent then this distribution tends toward uniformity in space if the freeway is either: (i) uncongested; or (ii) congested with queues on its on-ramps and enough inflow to cause the average freeway density to increase with time. In all other cases, however, including any recovery phase of a rush hour where the freeway’s average density...