Roads/Highways

The Spatial Evolution of Traffic Under the Two Wave Speed Assumption: A Shortcut Procedure and Some Observations

Daganzo, Carlos F.
1993

This paper describes the behavior of traffic in a homogeneous highway according to the hydrodynamic theory, in the special casewhere the flow-density relationship is triangular; i.e. when only two wave velocities exist. It presents an exact formula thatpredicts the vehicle that would be found at position x at time t, given the locations of all the vehicles at time zero. The formula, which does not require identification of the vehicle positions at intermediate times, automatically accounts for the creation and dissipation of any shocks. It can be used to calculate system performance...

Effect of Modeling Assumptions on Evolution of Queues in a Single Corridor

Daganzo, Carlos F.
Lin, Wei-Hua
1994

A qualitative description is presented of queuing patterns under an idealized scenario analogous to the evolution of traffic congestion during the morning peak hour in a long corridor leading to a single destination. The simplicity of the scenario allows the results to be verified independently by hand. Initially the corridor is assumed to consist of a single freeway. Traffic is generated at the freeway's many on-ramps during a short period and then is assumed to subside. Capacity limitations create queues on the ramps and the freeway, whose evolution is then described. A special...

A Continuum Theory of Traffic Dynamics for Freeways with Special Lanes

Daganzo, Carlos F.
1995

This paper presents a generalized theory of kinematic waves for freeways with two vehicle types and a set of lanes reserved for one of the vehicle classes. The theory is not restricted to freeways on which the special lanes are clearly identified by signs and pavement markings; e.g. for high occupancy vehicles. It may also apply if the restrictions are self-imposed, such as would occur on a freeway segment upstream of a busy off-ramp where the existing traffic naturally avoids the ‘far-side’ lanes. Of particular interest are oversaturated time periods because the original theory of...

Evaluation of Alternative AHS System Operating Concepts

Daganzo, Carlos F.
Cayford, Randall
Lin, Wei-Hua
1995

This paper focuses on technical and economic investigations of automated highway systems (AHS). It attempts to show that the actual viable implementation opportunities for AHS are scarce. The paper begins with an investigation that looks at realistic estimates of AHS capacity, interfacing with the local street system, and storage issues. The authors then identify criteria to help in determining which types of urban areas might be potential candidates for AHS technologies. Certain locations where AHS might be beneficial are identified, but doubt is raised regarding the extent of the...

Steady State Conditions on Automated Highways

del Castillo, Jose M.
Lovell, David J.
Daganzo, Carlos F.
1995

This paper is concerned with technical investigations of traffic operations on automated highways. Estimates are made of the steady-state capacity of such freeways, paying particular attention to the effect of entry and exit maneuvers. The possibility of scheduling departing vehicles appropriately into platoons to minimize extraneous maneuvers is investigated. Characteristics of urban areas likely to be candidates for automated freeways are discussed, and some shortcomings of automated freeways, vis-à-vis conventional freeways, are pointed out. Finally, some areas of future research needs...

A Simple Detection Scheme for Delay-Inducing Freeway Incidents

Lin, Wei-Hua
Daganzo, Carlos F.
1997

This paper describes a freeway incident detection scheme that does not rely on complicated theories. The procedure compares the occupancy information recorded by two neighboring loop detectors to determine whether an incident has occurred in the intervening segment, using a recipe that is directly related to an intrinsic property of delay-inducing incidents. The method, which can also signal the termination of a detected incident, assumes that any significant bottlenecks are located outside the segment in question: i.e. that the segment is “homogeneous”. Independent of complicated theories...

A Continuum Theory of Traffic Dynamics for Freeways with Special Lanes

Daganzo, Carlos F.
1997

This paper presents a generalized theory of kinematic waves for freeways with two vehicle types and a set of lanes reserved for one of the vehicle classes. The theory is not restricted to freeways on which the special lanes are clearly identified by signs and pavement markings; e.g. for high occupancy vehicles. It may also apply if the restrictions are self-imposed, such as would occur on a freeway segment upstream of a busy off-ramp where the existing traffic naturally avoids the ‘far-side’ lanes. Of particular interest are oversaturated time periods because the original theory of...

A Simple Physical Principle for the Simulation of Freeways with Special Lanes and Priority Vehicles

Daganzo, Carlos F.
Lin, Wei-Hua
Del Castillo, Jose M.
1997

This paper presents a simple physical principle that can be used to solve the kinematic wave problem for freeways with special lanes and priority vehicles. The principle is shown to yield the flows for all possible ‘Riemann problems’ arising in a homogeneous highway, so that its application in a simulation is equivalent to the Godunov ‘classic’ finite difference approximation method. The principle is appealing because its physical basis, unlike purely mathematical formulae, suggests a natural way in which boundary conditions for practical problems may be treated. Perhaps the IT principle...

The Netcell Simulation Package: Technical Description

Cayford, Randall
Lin, Wei-Hua
Daganzo, Carlos F.
1997

This report describes the NETCELL simulation package. NETCELL is a freeway network simulation program based on the cell transmission model which captures the dynamic evolution of multicommodity traffic over a freeway network with three-legged junctions in a way that is consistent with the hydrodynamic theory of highway traffic. NETVIEW is a graphical postprocessor for viewing NETCELL output files. This document discusses implementation of the programs in detail, including the cell representation for a freeway network with three-legged junctions, data and file structures, inputs and outputs...

Causes And Effects Of Phase Transitions In Highway Traffic

Daganzo, C. F.
Cassidy, M. J.
Bertini, R. L.
1997

It is shown that all the phase transitions in and out of freely flowing traffic reported earlier for a German site could be caused by bottlenecks, as are all the transitions observed at two other sites examined here. Furthermore, all the evidence indicates that bottlenecks cause these transitions in a predictable way, and no evidence is found that stoppages (jams) appear spontaneously in free flow traffic for no apparent reason. The most salient phenomena observed at all locations are explained in terms of a simple theory specific to traffic.