This research was funded by the National Institute for Transportation and Communities, or NITC, a program of TREC at Portland State University.
Intelligent transportation systems, Traffic engineering
This research seeks to understand the characteristics of transitions as freeway traffic changes from one state to another. This study addresses the features of two types of transitions; transitions near a merge and transitions along shock waves during the onsets and dissipations of queues at several freeway sites.
Individual vehicle trajectory data were analyzed for studying the transitions near a merge. The length of a transition zone was measured by analyzing the spatial changes in flow, density and speed along kinematic waves near a merge. It was found that the length of transition in terms of flow, density and speed were respectively around 90m, 120m and 180m indicating that the transition in flow occurs over a short distance while the transition in speed occurs in much longer space.
The dynamics of the transition zone were explored by analyzing the relationship among the transition durations, rates and various traffic and geometric variables at four freeway sites. Transition durations observed from the four sites vary from 10 to 24 minutes during the onsets of queues while the durations ranged from 10 to 30 minutes during the dissipations of the queues. At each site, formations and dissipations of queues displayed similar durations. Transition rates during the onsets of queues ranged from -7.6 to -2.2 kmph/min while they ranged from 2.0 to 6.2 kmph/min during the dissipations of queues. Some lane-specific features are observed in terms of initial speeds (just prior to transition), change in speed during transition, transition durations, and rates. It is also found that the structure of transition does not change in the absence of freeway interchanges as a queue expands and recedes. Finally, it is found that the transition rates tend to be larger upstream of an on-ramp while they tend to be smaller upstream of an off-ramp, indicating that inflows and outflows have different effects on transition characteristics.
Bertini, Robert L. and Soyoung Ahn. Characteristics of Transitions in Freeway Traffic. OTREC-RR-10-12. Portland, OR: Transportation Research and Education Center (TREC), 2010. http://dx.doi.org/10.15760/trec.150