Traffic Operations and Management

Decision-Making System for Freeway Incident Response Using Sequential Hypothesis Testing Methods

Madanat, Samer M.
Cassidy, Michael J.
Teng, Hua-Liang
Liu, Pen-Chi
1996

Recent research in advanced traffic management systems has emphasized incident detection and response to mitigate nonrecurring congestion. Existing incident response decision-making algorithms do not account for the expected losses associated with false alarms, undetected incidents, and delayed incident response. A freeway incident response decision-making system based on sequential hypothesis testing techniques is presented. The primary feature of this decision-making system is that it minimizes the sum of the expected losses associated with false response, nonresponse, and delayed...

Application of Ordered Probit Techniques to Analyze Ratings of Blissymbol Complexity

Soto, Gloria
Cassidy, Michael
Madanat, Samer
1996

This paper explores the application of ordered probit modeling, an econometric technique commonly used for the analysis of rating data in situations when respondents are asked to rate items (e.g., an object, service, or product), one at a time. To demonstrate the application of this methodology, an existing data set, originally collected to measure the perceived complexities for an array of Blissymbols, was used. Findings from the use of the ordered probit model are compared with those resulting from the earlier research that used regression procedures. Results from the use of ordered...

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.

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.

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...

Design Of A Machine Vision-based, Vehicle Actuated Traffic Signal Controller

Cassidy, Michael
Coifman, Benjamin
1998

This project presents a signal controller algorithm to capitalize on the extended information provided by wide-area detection at isolated intersections. Using computer simulation, different control strategies are evaluated and the performance of the proposed wide-area detection system with conventional signal controllers is compared. The results indicate that wide-area vehicle actuated (VA) control can yield significant improvements over conventional VA control strategies.

Some Observations of Highway Traffic in Long Queues

Smilowitz, Karen R.
Daganzo, Carlos F.
Cassidy, Michael J.
Bertini, Robert L.
1999

The arrival times of vehicles traveling southbound along a two-lane, bidirectional highway were recorded at eight neighboring locations upstream of a bottleneck caused by an oversaturated traffic signal. Cumulative curves constructed from these observations describe completely and in great detail the evolution of the resulting long queues. These queues formed directly upstream of the signal when the signal’s service rate fell below the southbound arrival rates, and never formed away from the bottleneck. The predictability of bottlenecks like the one studied here can be exploited to manage...

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...

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...