Roads/Highways

Effects of High Occupancy Vehicle Lanes on Freeway Congestion

Daganzo, Carlos F.
Cassidy, Michael J.
2008

Previous research on the effect of HOV (high occupancy vehicle) lanes on bottleneck flows is extended here to entire freeways using both theory and empirical evidence. The paper shows that if the flows of both high- and low-occupancy vehicles remain invariant before and after a freeway lane is converted to HOV use, then the freeway’s overall traffic density upstream of its bottlenecks is reduced – albeit less than expected – if the HOV lane is underutilized. As a result, HOV lanes can extend queues over longer distances. These expansions can be problematic if the queues’ expanded portions...

Smoothing Effect on Freeway Bottlenecks: Experimental Verification and Theoretical Implications

Cassidy, Michael J.
Jang, Kitae
Daganzo, Carlos F.
2009

Real data show that reserving a lane for carpools on congested freeways induces a smoothing effect that is characterized by significantly higher bottleneck discharge flows (capacities) in adjacent lanes. The effect arises because disruptive vehicle lane changing diminishes in the presence of a carpool lane. The effect is reproducible across days and freeway sites: it was observed, without exception, in all cases tested; and queueing analysis shows that the effect greatly reduces the times spent traveling on a freeway. The effect is so significant, in fact, that even a severely...

The Smoothing Effect of Carpool Lanes on Freeway Bottlenecks

Cassidy, Michael J.
Jang, Kitae
Daganzo, Carlos F.
2010

Real data show that reserving a lane for carpools on congested freeways induces a smoothing effect that is characterized by significantly higher bottleneck discharge flows (capacities) in adjacent lanes. The effect is reproducible across days and freeway sites: it was observed, without exception, in all cases tested. Predicted by an earlier theory, the effect arises because disruptive vehicle lane changing diminishes in the presence of a carpool lane. We therefore conjecture that smoothing can also be induced by other means that would reduce lane changing. The benefits can be large....

On the Stability of Freeway Traffic

Daganzo, Carlos F.
2010

Traffic flow theory 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. It is shown that 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, including any recovery phase of a rush hour where the freeway's average density declines, the distribution...

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...

Computation and Control of Solutions to the Burgers Equation Using Viability Theory

Aubin, J.-P.
Bayen, A.M.
Saint-Pierre, P.
2005

This paper presents a new approach which links the solution to the Burgers tracking problem to the concept of capture basin used in viability theory. This link enables the proof of the existence and uniqueness of the solution of the Burgers tracking problem. The Burgers tracking problem is linked to the Frankowska solutions of the Burgers equation. These results are easily extended to any first order hyperbolic partial differential equation (PDE) written in conservation law form, which is illustrated with the famous Lighthit-Whitham-Richards (LWR) PDE, known in highway traffic theory. The...

Optimal Sensor Requirements

Ban, Xuegang (Jeff)
Bayen, Alexandre M.
Chu, Lianyu
Danczyk, Adam
Herrera, Juan‐Carlos
2009

PATH Task ORder 6328 addresses the optimal deployment of traffic detectors on freeway to ensure that adequate information is collected at the lowest possible cost. The project team produced a study framework and tools that can be applied locally to test the sensitivity of traffic data quality to detectors location and spacing, and ultimately recommend a deployment plan.Various types of traffic detectors, including loop detectors, radars, toll tag readers and video cameras are deployed on highways. They provide the data needed to run traffic management applications such as ramp metering...

Real-Time Estimation of Pollution Emissions and Dispersion from Highway Traffic

Samaranayake, Samitha
Glaser, Steven D.
Holstius, David
Monteil, Julien
Tracton, Ken
Bayen, Alexandre
2014

Traffic-related air pollution is a serious problem with significant health impacts in both urban and suburban environments. Despite an increased realization of the negative impacts of air pollution, assessing individuals' exposure to traffic-related air pollution remains a challenge. Obtaining high-resolution estimates are difficult due to the spatial and temporal variability of emissions, the dependence on local atmospheric conditions, and the lack of monitoring infrastructure. This presents a significant hurdle to identifying pollution concentration hot spots and understanding the...

Adjoint-Based Optimization on a Network of Discretized Scalar Conservation Laws with Applications to Coordinated Ramp Metering

Reilly, Jack
Samaranayake, Samitha
Delle Monache, Maria
Krichene, Walid
Goatin, Paola
Bayen, Alexandre M.
2015

The adjoint method provides a computationally efficient means of calculating the gradient for applications in constrained optimization. In this article, we consider a network of scalar conservation laws with general topology, whose behavior is modified by a set of control parameters in order to minimize a given objective function. After discretizing the corresponding partial differential equation models via the Godunov scheme, we detail the computation of the gradient of the discretized system with respect to the control parameters and show that the complexity of its computation scales...

Hybrid Approach for Short-Term Traffic State and Travel Time Prediction on Highways

Allström, Andreas
Ekström, Joakim
Gundlegård, David
Ringdahl, Rasmus
Rydergren, Clas
Bayen, Alexandre M.
Patire, Anthony D.
2016

Traffic management and traffic information are essential in urban areas and require reliable knowledge about the current and future traffic state. Parametric and nonparametric traffic state prediction techniques have previously been developed with different advantages and shortcomings. While nonparametric prediction has shown good results for predicting the traffic state during recurrent traffic conditions, parametric traffic state prediction can be used during nonrecurring traffic conditions, such as incidents and events. Hybrid approaches have previously been proposed; these approaches...