Traffic Operations and Management

Reexamining Vehicle-Actuation Strategies at Isolated Signalized Intersections

Cassidy, Michael
Chuang, Yu-Hao
Vitale, Jeff
1996

This paper uses simulation to assess intersection performance under enhanced vehicle-actuated signal control. The enhanced strategies seek to: (1) terminate green time in such a way as to promote use of the clearance interval by discharging vehicles.

Bivariate Relations in Nearly Stationary Highway Traffic

Cassidy, Michael J.
1998

This paper demonstrates that reproducible bivariate relations exist among traffic variables, such as flow and occupancy, when traffic conditions are approximately stationary. The inspection of cumulative curves of vehicle arrival number and vehicle occupancy has revealed that sustained periods of nearly stationary conditions do arise in the traffic stream. By plotting average values of the data corresponding to each nearly stationary condition, well-defined relations are observed. These scatterplots of near-stationary data are contrasted with plots of data that were measured over...

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...

Observations at a Freeway Bottleneck

Cassidy, M. J.
Bertini, Robert L.
1999

Using transformed curves of cumulative vehicle count and cumulative occupancy, a study was conducted of traffic upstream and downstream of a bottleneck on a freeway in Toronto, Canada, located more than a kilometer downstream of a busy on-ramp. After diagnosing its location and the times that it remained active each day, the study focused on the traffic patterns that arose in each travel lane. It was observed that prior to the bottleneck's activation, vehicle lane-changing trends created extraordinarily high flows in the median (i.e., left-most) lane and that these high flows were...

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.....

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...