1 / 23

ITS Lab – May 27, 2008

Ramp Metering / SWARM Evaluation. ITS Lab – May 27, 2008. Outline. Project Overview Background Ramp Metering SWARM SWARM Evaluation Methodology Results Conclusions. Project Overview.

thadine
Download Presentation

ITS Lab – May 27, 2008

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ramp Metering / SWARM Evaluation ITS Lab – May 27, 2008

  2. Outline • Project Overview • Background • Ramp Metering • SWARM • SWARM Evaluation • Methodology • Results • Conclusions

  3. Project Overview • Using Archived Data to Measure Operational Benefits of a System-wide Adaptive Ramp Metering (SWARM) System • Research Partners • Portland State University ITS Lab • ODOT: Region 1, Research, and ITS • Portland Office of Transportation • FHWA

  4. Project Overview • Study Purpose • Measure benefits of adaptive ramp metering system • Improve understanding of system operation and help “tune” for better performance

  5. Ramp Metering Benefits • Minnesota Before/After Study (2000) • Ramp meters shut off for eight weeks • Congestion and accident rates increased • More delay for on-ramp traffic… • …but benefits system-wide • Increased travel time for short trips (ramp + mainline)… • …decreased travel time for longer trips. (Cambridge Systematics 2001, Kwon et al. 2001, Hourdakis and Michalopoulos 2002, and Levinson and Zhang 2002)

  6. Ramp Metering Background • Types of Ramp Metering • Pre-Timed • Traffic Responsive (Adaptive) Local Global Zhang et al., 2001

  7. SWARM • SWARM first implemented by CalTrans in Southern California • SWARM 1 = Global • SWARM 2a-c = Local • 2c = Portland • Occupancy at local and downstream detectors • Previous SWARM Evaluations • Benefits for mainline travel • Queues at 9 busiest on-ramps increased by over 40% • Combined local/global strategy most effective • Caltrans (2005), Pham et al (2002), MacCarley et al (2002)

  8. SWARM 1 (Global) Algorithm • Uses most restrictive of local and global metering rate

  9. SWARM Implementation • 1981: Pre-timed ramp meters implemented by ODOT • 2005-2006: Adaptive system (SWARM) implemented in phases by ODOT • SWARM is operating on six of seven metered freeway corridors in the Portland region • In general, 6-10 am, 1-7 pm weekdays

  10. Study Corridors • OR-217 SB • June 2006 • AM Peak • I-205 NB • Sept/Oct 2007 • AM & PM Peak • OR-217 NB • Nov/Dec 2007 • PM Peak OR-217 SB OR-217NB I-205 NB

  11. Methodology • Before and after study • 2 weeks pre-timed mode • 2 weeks SWARM mode • Control for various factors • Data sources • PORTAL: ODOT loop detector data, weather, incidents • Measurement of ramp queues • 5-Minute Video Samples (Pilot) • Programmable Logic Controllers (PLCs)

  12. Data Quality Pre-Timed SWARM • I-205 NB • Pre-Timed • SWARM • Implications? • Explanation? Communications infrastructure is critical for an adaptive system

  13. On Ramp Volume • On all corridors studied, SWARM allowed more vehicles onto the freeway than the pre-timed strategy • Why?

  14. Pre-Timed Metering Rate Table

  15. I-205 NB 9/21 (SWARM) (3) Metering Activation - at Powell, Johnson Creek, and Sunnyside under SWARM (5) Possible data quality issue (2) Metering Activation/ De-activation (Pre-Timed) (4) Metering activated earlier under SWARM (1) Study Boundaries(Gladstone-Division)

  16. 9/21 (SWARM) & 9/28 Pre-Timed Speeds dropped prior to activation Pre-Timed Metering Activation 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.

  17. 10/1 (Pre-Timed)& 9/17 (SWARM) (1) SWARM activation matches drop in speed (4) SWARM appears to implement a lower metering rate, responding to lower speeds. (2) But metering at Sunnyside (and likely Foster) activated later under SWARM than Pre-Timed (3) Slightly higher metering rates under SWARM than Pre-Timed

  18. Summary • SWARM allows more vehicles onto the freeway at each on-ramp. • Counter to ODOT’s initial assumptions • Pilot study on OR-217 SB demonstrated a tradeoff between decreased ramp delay and increased mainline delay • Could not conclude that higher on-ramp volumes were the sole cause. • SWARM’s earlier activation times reduce mainline delay under some conditions. • Adjustment of metering rates and other SWARM parameters is needed to improve performance of the system • Communications failures impact quality of SWARM operation • Tradeoff between frequently updating ramp metering plans, and increased need for maintenance and tuning w/adaptive system • Logging capabilities for SWARM/ATMS would make evaluation efforts easier • Ramp queue loop detectors, meter activation times, and actual metering rates set by the SWARM system

  19. Methodology (2) • 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.

  20. I-205 NB Performance Measures - AM • 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.

  21. I-205 NB Performance Measures - PM • 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.

  22. I-205 NB 9/28 (Pre-Timed) Meters de-activate while still congested. (2) Metering Activation/ De-activation (Pre-Timed) (1) Study Boundaries(Gladstone-Division)

More Related