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Variable Speed Limits

Making Work Zones Work Better Workshop Orlando, Florida 17 Sept. 03 Davey Warren Office of Safety Programs Federal Highway Administration . Variable Speed Limits. Presentation Overview. What is a variable speed limit? How do variable speed limits work?

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Variable Speed Limits

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  1. Making Work Zones Work Better Workshop Orlando, Florida 17 Sept. 03 Davey Warren Office of Safety Programs Federal Highway Administration Variable Speed Limits

  2. Presentation Overview • What is a variable speed limit? • How do variable speed limits work? • Objectives of variable speed limit system • Work Zone Tests • Lessons learned • Future products and additional information

  3. What is a Variable Speed Limit (VSL)? • Speed limit changes with changing conditions 1950

  4. Part-time Speed Limit Work Zone

  5. Focus of presentation • Modern systems change the speed limits in real time: • Traffic conditions • Adverse weather conditions • Road surface conditions • Work Zones 1960

  6. Computer controlled limits

  7. Variable Speed Limit System Components • traffic and speed detectors • variable speed signs • microprocessor • communication • environmental sensors • base station for recording speed limit changes

  8. Why Use Variable Speed Limits?

  9. Objectives • Increase compliance • Improve safety • More efficient use of highway • Less burdened justice system • Responsive to dynamic conditions • Provide real time information

  10. Variable Speed Limit Applications • General VSL • Winter Weather and Adverse Road Conditions • Fog • Congestion • Work Zones

  11. General VSL Examples • NJ Turnpike • I-40 New Mexico • Germany Characteristics • Typically cover longer stretches of roadway • Broad range of input criteria for speed limit decision (traffic speed, volume, crashes, congestion, construction, ice, snow, fog, etc.)

  12. I-40 New Mexico • fully automated • maximum speed limit • constrained by NMSL • minimum speed limit • downstream hazard warning • roadside station after each interchange

  13. Average Speeds and Variable Limit Over 24 hr

  14. N.M. Automated Speed Control Logic Smooth Mean Speed +/-

  15. Congestion 1960 • Examples Lodge Freeway, MI M25, UK Netherlands • Characteristics • Cover stretches of congested roadways • Speeds set to reflect traffic conditions • Slow traffic approaching backups

  16. Winter Weather and Road Conditions • Examples I-90, Washington E18, Finland I-40, Arizona • Characteristics • Cover longer stretches of weather-susceptible roadways • Speeds set to reflect roadway/weather/visibility conditions

  17. Fog • Examples I-75, Tennessee I-80, Nevada F-6, Australia A 16, Netherlands • Characteristics • Typically deployed in areas that experience highly variable, severe fog • Speed and visibility sensors

  18. VSL in Work Zones • Dynamic conditions in work zones make them excellent candidates for VSL • FHWA is sponsoring 3 field tests of VSL in work zones • Michigan • Maryland • Virginia

  19. Field Test Objectives • Objectives: • Deploy practical variable speed limit systems in work zones • Evaluate the effectiveness of the systems on: • Speed limit compliance • Credibility of speed limits • Improved Safety • Improved Traffic flow

  20. Michigan’s VSL System • Four deployments to date • Where: • 19-mile work zone • I-96 near Lansing • ADT 29k – 53k • (over 10% trucks) • When: late May – August 2002 • Duration: Short – All less than 1 week

  21. I-96 Michigan • 6-7 variable speed limit trailers • RTMS Traffic detector • Solar power • Controller with RF communication • LED speed display • ½-1 mi spacing • line of sight communication • 70 to 40 mi/h • Based on prevailing speed • Max based on nature of road work • Pagers used to transmit speed limit changes to police

  22. Michigan’s Speed Control Logic

  23. Michigan’s VSL System • Preliminary Results: • Better compliance • More uniform speeds during off-peak • Travel times reduced • Greater speed reduction at crossover • RTMS accurate for volume but marginal for speed • Trailers can be set-up within 10 minutes

  24. Maryland’s Work Zone VSL • VSL Trailers – 4 • Radar unit for speed • Queue Detector Trailers – 2 • Variable Message Signs on Trailers – 2 • Base Unit – Central Control (CHIPS System Trailer) – 1

  25. Maryland’s VSL Algorithms • Logic: • User selectable percentile speed • Percentile can vary depending on whether workers present or not • User can specify times to switch percentile • Speed limit will be updated no more frequently than every 2 minutes. • 2 other candidate algorithms programmed • Tweener • Oz

  26. Maryland’s VSL System Status • Status: • Completed pre-deployment testing and accepted equipment • First deployment will occur in the next month • The second deployment has yet to be scheduled

  27. Lessons Learned • Engineering • Perform “off-site” testing on a real road • Eliminate unnecessary fluctuations in limit • May need to change as often as once a minute • Need signs on both sides of road with 3 or more lanes • Implementation • Make sure that all stakeholders are on board and working towards common goals • Don’t try to do everything all at once – start with something easy • Work closely with the media; have only 1 or 2 PR people for the media to contact • Be flexible (expect the unexpected)

  28. Summary • VSL being used around the world to help manage speed and improve safety • VSL seems to be particularly appropriate for work zones • Enforcement remains an issue • More and better data needed on effectiveness

  29. Additional Information http://www.itsdocs.fhwa.dot.gov/itsweb/welcome.htm • Examples of Variable Speed Limit Applications (EDL#12164) • Safety Applications of ITS in Rural Areas (EDL#13609 ) http://gulliver.trb.org/publications/nchrp/nchrp_lrd_47.pdf • NCHRP Legal Research Digest 47: Judicial Enforcement of Variable Speed http://safety.fhwa.dot.gov/fourthlevel/pdf/poynton1.pdf • Controlled Motorways: Variable Speed Limits on the M-25, UK http://safety.fhwa.dot.gov/fourthlevel/ppt/Warren_Vsl.ppt • Variable Speed Limit slide show Future Products • NCHRP 3-59 Variable Speed Limit Implementation Issues (2004) • Field Test Evaluation Cross-Cutting Study Report (2004)

  30. Questions Davey Warren FHWA HSA-20 400 7th Street, SW Washington, DC 20590 202-366-4668 davey.warren@fhwa.dot.gov

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