Empirical Evaluation of Adaptive Ramp Metering Along Two Freeway Corridors in Portland, Oregon

This paper describes the System-Wide Adaptive Ramp Metering (SWARM) system that has been implemented in the Portland, Oregon metropolitan area, replacing the previous pre-timed ramp-metering system that had been in operation since 1981. SWARM has been deployed on six major corridors and operates during the morning and afternoon peak hours. The authors report on the results of a “before” and “after” evaluation of the performance of two freeway corridors as part of ongoing efforts to measure the benefits of the new SWARM system. The study used the existing regional data, surveillance and communications infrastructure in addition to a regional data archive system. The findings revealed mixed results when comparing the selected performance metrics to the previously-used, pre-timed system. For the Interstate- 205 corridor, the results were generally positive: in the morning peak period, SWARM operation resulted in decreased mainline delay and decreased variability in the delay; For the afternoon peak period, improvements were also found with the exception of moderately congested days, which saw an increase in mainline delay. On the Oregon State Route 217, however, significant increases were found in overall average delay. Reliability also decreased under SWARM for this corridor. The authors suggest that the differences in SWARM performance may be due to the differences between the two roads. OR-217 is a relatively short freeway (7 miles) bounded on both ends by freeway-to-freeway interchanges. The ramp spacing is generally short (0.75 mile average) and the freeway contains numerous auxiliary lane drops and adds. The I-205 corridor is unbounded, has greater ramp spacing (1.07 mile average), and maintains three through lanes. They also discuss the potential impact of data communication failures. The authors conclude by recommending the development of an ongoing ramp metering performance reporting system.


  • English

Media Info

  • Media Type: CD-ROM
  • Features: Figures; Maps; References; Tables;
  • Pagination: 11p
  • Monograph Title: ITS Connections: Saving Time. Saving Lives

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Filing Info

  • Accession Number: 01142006
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Oct 5 2009 7:07AM