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5/15/2008

Using Archived Data to Measure Operational Benefits of a System-wide Adaptive Ramp Metering (SWARM) System TAC Meeting. 5/15/2008. Outline. Data Quality Ramp Flow Results Performance measures Comparison by level of congestion Methodology Two “highly congested” days (9/28 & 9/21)

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5/15/2008

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  1. Using Archived Data to Measure Operational Benefits of a System-wide Adaptive Ramp Metering (SWARM) SystemTAC Meeting 5/15/2008

  2. Outline Data Quality Ramp Flow Results Performance measures Comparison by level of congestion Methodology Two “highly congested” days (9/28 & 9/21) Two “moderately congested” days (10/1 & 9/17) Conclusions & Recommendations

  3. Data Quality 3 • OR-217 NB significantly improved • Compared to I-205 NB or OR-217 Pilot Study • Infrastructure improvements appear to have been effective • Pre-timed data quality still better than SWARM • ~1% vs. ~5% failure rate • Several problematic stations on I-205 NB • Clackamas Highway, Glisan • Sunnybrook, Powell

  4. I-205 NB Data Quality – PM Pre-Timed SWARM AM is similar

  5. OR-217 NB Data Quality – PM Pre-Timed SWARM 5

  6. On Ramp Volume • On all corridors studied, SWARM allowed more vehicles onto the freeway than the pre-timed strategy • Flow increased slightly at most of the busy ramps • As discussed at the previous TAC meeting, SWARM has a single maximum rate, believed to be the highest pre-timed rate and could in theory apply this rate at any time.

  7. Methodology (1/2) • For each ramp, each day classified as uncongested or congested • Noted as “lightly” congested if < six 5-min periods (30 minutes) matched criteria. • Evaluation criteria • I-205 NB: Occupancy > 18% and/or speeds < 45 mph • OR-217 NB: Occupancy > 18% and/or speeds < 35-40 mph • Duration of these conditions • Extent of congestion along the study corridor • Days grouped into lightly, moderately, or highly congested • Amount of delay a secondary criteria; used to group days with most congestion.

  8. Methodology (2/2) 8 • Our determination of congested conditions was somewhat subjective • Based on fundamental traffic flow relationships • Flow (Volume) • Density (~Occupancy) • Speed The figure shows the expected relationships between the three variables: flow (volume), speed, and occupancy. In the plots from the freeway data, you can see these general relationships in the data. We used the fundamental shapes to define the thresholds for congestion. In the flow-density curve, data to the right of kcap is in the congested regime; we determined occupancy and speed values that generated congested flow.

  9. I-205 NB AM Period Performance Measures • Excluding the single highly congested day under Pre-Timed (10/4), delay under SWARM was about 5 percent lower. • We believe the lower level of delay reflects more vehicles on the freeway, given higher on ramp flows. Given lower overall freeway volumes in the AM, there isn’t the adverse effect on mainline performance that there appears to be in the PM.

  10. I-205 NB PM Period Performance Measures • Excluding the least congested day, the average delay for “moderately congested” days was nearly 30 percent greater under SWARM operation (comparable to the PM period on OR-217). There were four each of these “moderate” days in the pre-timed and SWARM periods. • SWARM performed better than the pre-timed system on the most highly congested days, which we attribute to earlier metering activation times on those days.

  11. OR-217 NB Performance Measures 11 • Under SWARM, there were no comparable days to the least congested pre-timed days. • Excluding the least congested days, the average delay for “moderately congested” days was nearly 30 percent greater under SWARM operation (a comparable figure to the PM period on I-205). There were three each of these “moderate” days in the pre-timed and SWARM periods. • Comparing two “highly” congested days, delay was about 4.5 percent lower under SWARM than pre-timed. • There was one “very highly” congested days under pre-timed and three under SWARM. On average, delay was about 16 percent greater under SWARM on those days.

  12. OR-217 SB (Pilot) Performance Measures 12

  13. I-205 NB Corridor Diagram • Next graphics focus on Sunnyside - Foster

  14. I-205 NB, PM, Highly Congested9/28 (Pre-Timed) & 9/21 (SWARM) Note: SWARM Metering Activation Data not collected at Foster Metering activated earlier under SWARM Despite a slightly higher metering rate, SWARM’s earlier activation appeared to delay the onset of congested speeds and allowed for higher and more stable mainline flows.

  15. I-205 Highly Congested Comparison • 9/28 – Pre-Timed Metering Activation/ De-activation (Pre-Timed) Study Boundaries(Gladstone-Division)

  16. I-205 Highly Congested Comparison • 9/21 – SWARM Metering Activation - at Powell, Johnson Creek, and Sunnyside under SWARM Metering Activation/ De-activation (Pre-Timed) Metering activated earlier under SWARM

  17. I-205 NB, PM, Moderately Congested10/1 (Pre-Timed) & 9/17 (SWARM) Metering at Sunnyside (and likely Foster) activated later under SWARM than Pre-Timed. Higher metering rates under SWARM than Pre-Timed SWARM appears to implement a lower metering rate

  18. I-205 NB Moderately Congested Comparison • 10/1 – Pre-Timed

  19. I-205 NB Moderately Congested Comparison • 9/17 – SWARM

  20. Conclusions & Recommendations (1/2) • Data Quality • Issues under SWARM impacted sample size and ability to compare like days • Communications failures may affect SWARM’s ability to compute appropriate metering rates (local and global) • Clackamas Highway and Glisan (1st tier), Powell and Sunnybrook (2nd tier) have the most significant communications issues on I-205 NB. • Infrastructure improvements on OR-217 NB appear very effective

  21. Conclusions & Recommendations (2/2) • SWARM let more vehicles onto the freeway, and did not appear to adjust the metering rate to traffic conditions quickly enough, even when rate was higher than the most restrictive. • While not quantified in the regional study, pilot study conclusion that ramp delay was reduced likely applies to regional study corridors • SWARM appears to perform better on days with the most significant amount of delay, which we attribute in part to earlier metering activation times. • Adjustment of metering rates and other SWARM parameters may improve performance of the system • Recall discussion at last TAC meeting about SWARM applying maximum rate from pre-timed plans at any time. • Adaptive system reduces ODOT workload in need to frequently update ramp metering plans • Incorporating logging capabilities for SWARM/ATMS would make evaluation efforts easier, particularly ramp queue loop detectors, meter activation times, and actual metering rates set by the SWARM system.

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