Traffic Operations and Management

Some Traffic Features at Freeway Bottlenecks

Cassidy, Michael J.
Bertini, Robert L.
1999

Observations from two freeway bottlenecks in and near Toronto, Canada indicate that the average rate vehicles discharge from a queue can be 10% lower than the flow measured prior to the queue's formation. Absent any influences from downstream, the queue discharge flows exhibited nearly stationary patterns that alternated between higher and lower rates. These alternating flow patterns were especially evident at one of the two sites, although the feature occurred at both sites during periods that immediately followed the onset of upstream queueing; i.e. a queue's formation was always...

Possible Explanations of Phase Transitions in Highway Traffic

Daganzo, C. F.
Cassidy, M. J.
Bertini, R. L.
1999

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. The evidence suggests that bottlenecks cause these transitions in a predictable way, and does not suggest that stoppages (jams) appear spontaneously in free flow traffic for no apparent reason. It is also shown that many of the complicated instability phenomena observed at all locations can be explained qualitatively in terms of a simple Markovian theory specific to traffic...

An Observed Traffic Pattern in Long Freeway Queues

Cassidy, M. J.
Mauch, Michael
2001

A simple exercise in data analysis showed that, in queued traffic, a well-defined relation exists between the flow on a homogeneous freeway segment and the segment’s vehicle accumulation. The exercise consisted of constructing cumulative vehicle arrival curves to measure the flows and densities on multiple segments of a queued freeway. At this particular site, each interchange enveloped by the queue exhibited a higher on-ramp flow than off-ramp flow and as a consequence, motorists encountered a steady improvement in traffic conditions (e.g., reduced densities and increased speeds) as they...

Recent Findings on Simple Attributes of Freeway Queue Formation and Propagation

Cassidy, M. J.
2001

Traffic observations at, and upstream of, some freeway bottlenecks are presented in three parts. The first two of these are of bottleneck activations: at a bottleneck formed by a diverge and at another by a merge, traffic features that gave rise to queueing are displayed. These were subtle and their identification relied upon processing the traffic data in special ways. But once diagnosed, the bottleneck causes proved to be uncomplicated and opportunities exist for mitigating them using simple traffic control strategies. Also presented (and likewise benefiting from special treatment of the...

Vehicle Reidentification and Travel Time Measurement. I. Congested Freeways

Coifman, B.
Cassidy, M.
2001

The paper presents an algorithm for matching individual vehicles measured at a freeway detector with the vehicles' corresponding measurements taken earlier at another detector located upstream. Although this algorithm is potentially compatible with many vehicle detector technologies, the paper illustrates the method using existing dual-loop-detectors to measure vehicle lengths. This detector technology has seen widespread deployment for velocity measurement. Since the detectors were not developed to measure vehicle length, these measurements can include significant errors. To overcome this...

Middleware for Cooperative Vehicle-Infrastructure Systems

Manasseh, Christian
Sengupta, Raja
2008

Middleware has emerged as an important architectural component in supporting distributed applications. The role of middleware is to present a unified programming model to application writers and to mask out problems of heterogeneity and distribution. Mobile sensors fall into the space of distributed systems that suffer from isolated data sources, heterogeneous communication infrastructure and varying application requirements. In this report, we provide a middleware architecture that addresses the needs of a distributed system made of mobile sensors in general and discuss the implementation...

Identification and Integration of Commercial Heavy Vehicle Retarders

Druzhinina, Maria
Moklegaard, Lasse
Stefanopoulou, Anna G.
2002

This report describes the development and experimental validation of a coordination scheme between friction and discretely variable compression brakes for a Class 8 Freightliner truck used as a development platform in the California PATH program. The coordination scheme that we developed maintains the speed tracking performance of the nominal PID controller which was originally designed by the UCLA team for the case of friction brakes only.....

Some Observed Details of Freeway Traffic Evolution

Windover, John R.
Cassidy, Michael J.
2001

Certain details of traffic evolution were studied along a 2 km, homogenous freeway segment located upstream of a bottleneck. By comparing (transformed) cumulative curves constructed from the vehicle counts measured at neighboring loop detectors, it was found that waves propagated through queued traffic like a random walk with predictable statistical variation. There was no observed dependency of wave speed on flow. As such, these waves neither focused nor fanned outward and shocks arose only at the interfaces between free-flowing traffic and the back of queues. Although these traffic...

Documentation of the Irvine Integrated Corridor Freeway Ramp Metering and Arterial Adaptive Control Field Operational Test

McNally, M. G.
Moore, II, James E.
MacCarley, C. Arthur
2001

A systematic evaluation of the performance and effectiveness of a Field Operational Test (FOT) of an integrated corridor-level adaptive control system was attempted from fall 1994 through spring 1999 in the City of Irvine, California. The FOT was conducted by a consortium consisting of the California Department of Transportation (Caltrans), the City of Irvine, and two private sector consultants, National Engineering Technologies, Inc. (NET) and Farradyne Systems, Inc. (FSI, now PB/FSI), with the City of Irvine as the lead agency. The FOT was cost-share funded by the Federal Highway...

Freeway Traffic Oscillations: Observations And Predictions

Mauch, Michael
Cassidy, Michael J.
Taylor, Michael A. P.
2002

Freeway traffic was observed over multiple days and was found to display certain regular features. Oscillations arose only in queues; they had periods of several minutes; and their amplitudes stabilized as they propagated upstream. They propagated at a nearly constant speed of about 22 to 24 kilometers per hour, independent of the location within the queues and the flow measured there; this was observed for a number of locations and for queued flows ranging from about 2,000 to 850 vehicles per hour per lane. The effects of the oscillations were not felt downstream of the bottleneck. Thus,...