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FHWA Localized Bottleneck Reduction Program

Case Study

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Contact Information: Neil Spiller at Neil.Spiller@dot.gov

An overhead ramp signal with message "One Car Per Green"

Location – Minneapolis-St. Paul, Minnesota

Results of 2001 study of Ramp Metering Effectiveness

In September 2000, all 430 ramp meters were turned off in the Twin Cities region in response to a mandate from the MN State Legislature, following citizen complaints and questions raised by State Senator Dick Day; namely, do ramp meters work?

Objectives

  • To fully explore effectiveness of ramp meters; meter "wait time" was also a key concern
  • To respond to citizen's questions and identify public perception of ramp metering
  • To involve a citizens advisory board to ensure credibility of the study

Process and Findings

Cambridge Systematics was hired by MnDOT to perform the study, inclusive of getting pre-study data and incorporating any/all citizen input and ensuring a transparent process. Five weeks of "before" speed and crash data, et al, was recorded. The ramps were shut off for a pre-determined "transition" period and then turned back on for five weeks of "after" data gathering.

  • Without meters
    • A 9% reduction in freeway volume; a 22 % increase in travel times; a 26% increase in crashes (even after adjusting for prior seasonal rates)
    • Most survey respondents believed traffic had worsened
  • After the study: 20% wanted meters left off; 10% want them "returned"; 70% want modifications

Lessons Learned / Changes Implemented

  • Neither "all" nor "nothing" was deemed best, but a new, modified approach was adopted:
    • Fewer meters than before the study were turned back on (location candidacy was tightened and superfluous meters were removed)
    • Hereafter, meters would wait no more than 4 minutes on local ramps or 2 minutes on freeway-to-freeway ramps
    • Vehicles queued back to city streets will be "released" (meters temporarily shut off) and meter operation will better-respond to congestion-only times via improved use of detectors
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