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Using PeMS Data to Empirically Diagnose Freeway Bottleneck Locations in Orange County, California
Research conducted
by Aaron Myton and Robert L. Bertini
ABSTRACT: In order to improve freeway modeling and operations, it is important to understand how traffic conditions evolve in
both time and space. The widespread availability of freeway sensor data makes detailed operational analysis
possible in ways that were not available in the past. Inspired by several other studies of a six-mile segment of
Interstate 405 in Orange County, California, this paper’s objective is to describe the evolution of traffic conditions
over one morning peak period using inductive loop detector data, including vehicle count and lane occupancy
measured at 30-second intervals. Using cumulative curves of vehicle count and occupancy, transformed in ways that
enhanced their resolution, ten bottleneck activations were identified in time and space over one morning peak
period. Upon bottleneck activation, queue propagation was observed in generally predictable ways. Bottleneck
outflows were carefully measured only while the bottlenecks were active—that is, while queued conditions persisted
upstream and unqueued (freely-flowing) conditions prevailed downstream. When bottlenecks were activated
immediately following freely-flowing conditions, outflow reductions were observed upon queue formation. These
reductions were consistent with previous studies. The study was limited in that only one day’s data were analyzed,
and ramp data were not available on the day analyzed. Future research will include further analysis of the same site
using more recent data now that ramp counts are available in the PeMS database. Understanding the mechanisms
that lead to bottlenecks activation is a critical step toward improving the understanding of how freeways function
and is necessary for addressing operational issues. This clear understanding provides a foundation for determining
ramp metering rates and addressing the freeway characteristics that cause bottlenecks to form.
Publications
Bertini, R.L. and Myton, A. “Using PeMS Data to Empirically Diagnose Freeway Bottleneck Locations in Orange County, California.” Transportation Research Record: Journal of the Transportation Research Board, Washington , D.C., 2004. (In Press).
Presentation
Myton, A. "Using PeMS Data to Empirically Diagnose Freeway Bottleneck Locations in Orange County, California. Presented at the 84th Annual Meeting of the Transportation Research Board, Washington, D.C., January
M.S. Project
I-405 Freeway Bottleneck Analysis
By A. Myton, M.S. Project, Department of Civil Environmental Engineering, Portland State University, 2004.
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