NCDOT I-540 Ramp Metering in Raleigh, Lessons Learned. Meredith McDiarmid NCDOT Transportation Mobility and Safety October 2018

Transcription

1 NCDOT I-540 Ramp Metering in Raleigh, Lessons Learned Meredith McDiarmid NCDOT Transportation Mobility and Safety October 2018

2 What is Ramp Metering? Traffic signals on the freeway onramp Controls flow and promotes safe merging Benefits: Reduce Congestion Safety Source: FHWA 2

3 NCDOT I-540 On-ramp Signals Project First Ramp Metering in NC 4 on-ramp signals Intelight software STOC managing ITRE evaluating Stages: NCDOT Project Planning, Guidance from GDOT Fixed flowrates Sept. 27, 2017 Traffic responsive Dec. 13, 2017 System-wide traffic responsive: TBD 3

4 Operational Performance After 6 months: Average congestion duration reduced by 22 minutes (24%) Travel times reduced for 70% of all drivers on mainline and ramps Traffic volumes on mainline stayed the same increased slightly 4

5 Lessons Learned: Data Collection Speed and Travel Time Data Third-party probe data (HERE) Travel Time sensors (Bluetooth) Volume Data NCDOT volume sensors Intelight ramp meter detectors ITRE manual count (from CCTV) Lessons learned: Need baseline volume data collection, before metering begins (!) Need data on arterial existing conditions Diversion? Traffic backups from meters? Source: Iteris ipems, derived from HERE probe data. 5

6 Lessons Learned: Design Consider operations in planning and design Stop Bar: Lane drop arrow placement Tradeoff: stop bar placement for merging vs. queue storage Falls of Neuse Ramp: Lane drop arrow placement Source: Raleigh News and Observer drone footage, article 3/29/2018 6

7 Lessons Learned: Ramp Queue Detectors Ramp queue detectors: Consider intermediate queue detection Place excessive queue sensors further back Source: M-0446 Ramp Metering Feasibility Study for Durham and Wake Counties. Atkins Typical Design Criteria. Final Report. Mar

8 Ramp Queue Detectors (more) Use separate ramp queue detector NB-LT movement SB-RT movement I-540 On-Ramp Signal at Six Forks Rd, showing separate feeder lanes by turning movement. Source: I-540 Ramp Meter Standard Specifications, Atkins,

9 Challenge: Complex Software Settings Intelight MaxView Vendor needs to provide more training and documentation Determine: Threshold Table for traffic responsive metering rate to mainline flows Active Queue settings for ramp metering rate adjustments due to queues at ramps Challenge: Getting the data from the system Intelight provides access to some data via external reports Detector volumes Ramp meter signal active metering rate logs Suggestion: Operator-centric dashboard Ramp queuing Mainline performance indicators Example: MaxView settings for Active Queue 9

10 Challenge: Operational Roles Be clear about role of software vendor: Who will design and maintain the metering plans and software settings Who will do the dayto-day operation? Winter weather NCDOT Statewide Traffic Control Center, Raleigh 10

11 Challenges and Lessons Learned: Equipment and Comm. Must be able to see on-ramp signals Network bandwidth for video Modem not ideal Project Special Provisions: spare parts: Controller Modem I/O module Detector cards Wiring challenges on opening day Prior to activation do a LIVE field test! 11

12 Challenge: Managing Expectations How to sell the case for Ramp Metering to stakeholders?: (city, public, and MPO) Don t promise to flush the ramps to avoid queue spillback Don t set the expectations of capacity benefits too high 12

13 Next Steps Work with City of Raleigh on arterial signal timing for smooth operations with on-ramp signals 13

14 Summary On-ramp signals: a 60-year history with proven benefits safety increased throughput reduced overall travel time I-540 WB on-ramp signals are the first in the state of NC Initial findings: moderate improvement Steep learning curve for agencies May want to consider design exceptions Keep operations in mind from the beginning, and all through the project 14