594 research outputs found
Analysis of kinematic waves arising in diverging traffic flow models
Diverging junctions are important network bottlenecks, and a better
understanding of diverging traffic dynamics has both theoretical and practical
implications. In this paper, we first introduce a continuous multi-commodity
kinematic wave model of diverging traffic and then present a new framework for
constructing kinematic wave solutions to its Riemann problem with jump initial
conditions. In supply-demand space, the solutions on a link consist of an
interior state and a stationary state, subject to admissible conditions such
that there are no positive and negative kinematic waves on the upstream and
downstream links respectively. In addition, the solutions have to satisfy
entropy conditions consistent with various discrete diverge models. In the
proposed analytical framework, kinematic waves on each link can be uniquely
determined by the stationary and initial conditions, and we prove that the
stationary states and boundary fluxes exist and are unique for the Riemann
problem of diverge models when all or partial of vehicles have predefined
routes. We show that the two diverge models by Lebacque and Daganzo are
asymptotically equivalent. We also prove that the supply-proportional and
priority-based diverge models are locally optimal evacuation strategies. With
numerical examples, we demonstrate the validity of the analytical solutions of
interior states, stationary states, and corresponding kinematic waves. This
study presents a unified framework for analyzing traffic dynamics arising in
diverging traffic and could be helpful for developing emergency evacuation
strategies.Comment: 48 pages, 14 figure
Stability and bifurcation in network traffic flow: A Poincar\'e map approach
Previous studies have shown that, in a diverge-merge network with two
intermediate links (the DM network), the kinematic wave model always admits
stationary solutions under constant boundary conditions, but periodic
oscillations can develop from empty initial conditions. Such contradictory
observations suggest that the stationary states be unstable. In this study we
develop a new approach to investigate the stability property of traffic flow in
this and other networks. Based on the observation that kinematic waves
propagate in a circular path when only one of the two intermediate links is
congested, we derive a one-dimensional, discrete Poincar\'e map in the out-flux
at a Poincar\'e section. We then prove that the fixed points of the Poincar\'e
map correspond to stationary flow-rates on the two links. With Lyapunov's first
method, we demonstrate that the Poincar\'e map can be finite-time stable,
asymptotically stable, or unstable. When unstable, the map is found to have
periodical points of period two, but no chaotic solutions. Comparing the
results with those in existing studies, we conclude that the Poincar\'e map can
be used to represent network-wide dynamics in the kinematic wave model. We
further analyze the bifurcation in the stability of the Poincar\'e map caused
by varying route choice proportions. We further apply the Poincar\'e map
approach to analyzing traffic patterns in more general and beltway
networks, which are sufficient and necessary structures for network-induced
unstable traffic and gridlock, respectively. This study demonstrates that the
Poincar\'e map approach can be efficiently applied to analyze traffic dynamics
in any road networks with circular information propagation and provides new
insights into unstable traffic dynamics caused by interactions among network
bottlenecks.Comment: 31 pages, 10 figures, 2 table
Kinematic Wave Models of Network Vehicular Traffic
The kinematic wave theory, originally proposed by (Lighthill and Whitham,
1955b; Richards, 1956), has been a good candidate for studying vehicular
traffic. In this dissertation, we study kinematic wave models of network
traffic, which are expected to be theoretically rigorous, numerically reliable,
and computationally efficient.
For traffic systems with inhomogeneous links, merges, diverges, or mixed-type
vehicles, we study the kinematic waves in their Riemann solutions and develop
numerical solution methods of the Godunov type and the supply-demand type.
For a network traffic system, we propose a multi-commodity kinematic wave
(MCKW) model and an implementation of it. The model observes First-In-First-Out
principle in the order of a time interval and is numerically convergent.
Further, we apply this simulation model to study equilibrium states and
periodic waves in road networks.
Finally, we summarize our work and discuss future research directions.Comment: Ph.D. Dissertation. UC Davis. 218 pages, 12 tables, 61 figure
The State-of-the-art of Coordinated Ramp Control with Mixed Traffic Conditions
Ramp metering, a traditional traffic control strategy for conventional
vehicles, has been widely deployed around the world since the 1960s. On the
other hand, the last decade has witnessed significant advances in connected and
automated vehicle (CAV) technology and its great potential for improving
safety, mobility and environmental sustainability. Therefore, a large amount of
research has been conducted on cooperative ramp merging for CAVs only. However,
it is expected that the phase of mixed traffic, namely the coexistence of both
human-driven vehicles and CAVs, would last for a long time. Since there is
little research on the system-wide ramp control with mixed traffic conditions,
the paper aims to close this gap by proposing an innovative system architecture
and reviewing the state-of-the-art studies on the key components of the
proposed system. These components include traffic state estimation, ramp
metering, driving behavior modeling, and coordination of CAVs. All reviewed
literature plot an extensive landscape for the proposed system-wide coordinated
ramp control with mixed traffic conditions.Comment: 8 pages, 1 figure, IEEE INTELLIGENT TRANSPORTATION SYSTEMS CONFERENCE
- ITSC 201
Vision-Based Lane-Changing Behavior Detection Using Deep Residual Neural Network
Accurate lane localization and lane change detection are crucial in advanced
driver assistance systems and autonomous driving systems for safer and more
efficient trajectory planning. Conventional localization devices such as Global
Positioning System only provide road-level resolution for car navigation, which
is incompetent to assist in lane-level decision making. The state of art
technique for lane localization is to use Light Detection and Ranging sensors
to correct the global localization error and achieve centimeter-level accuracy,
but the real-time implementation and popularization for LiDAR is still limited
by its computational burden and current cost. As a cost-effective alternative,
vision-based lane change detection has been highly regarded for affordable
autonomous vehicles to support lane-level localization. A deep learning-based
computer vision system is developed to detect the lane change behavior using
the images captured by a front-view camera mounted on the vehicle and data from
the inertial measurement unit for highway driving. Testing results on
real-world driving data have shown that the proposed method is robust with
real-time working ability and could achieve around 87% lane change detection
accuracy. Compared to the average human reaction to visual stimuli, the
proposed computer vision system works 9 times faster, which makes it capable of
helping make life-saving decisions in time
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