Variable Speed Limits Making Work Zones Work Better

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

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

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

Part-time Speed Limit Work Zone

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

Computer controlled limits

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

Why Use Variable Speed Limits?

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

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

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. )

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

Average Speeds and Variable Limit Over 24 hr

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

Congestion • Examples Lodge Freeway, MI M 25, UK Netherlands • Characteristics • Cover stretches of congested roadways • Speeds set to reflect traffic conditions • Slow traffic approaching backups 1960

Winter Weather and Road Conditions • Examples I-90, Washington E 18, Finland I-40, Arizona • Characteristics • Cover longer stretches of weather-susceptible roadways • Speeds set to reflect roadway/weather/visibility conditions

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

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

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

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

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

Michigan’s Speed Control Logic Profile 1 Workers 2 Workers 3 No Work Unprotected Present Activity L. O. Threshold - 0% 50 60 70 H. O. Threshold – 70% 40 40 40 v < 40 40 40 ≤ v < 43 45 45 45 43 ≤ v < 48 50 50 50 48 ≤ v < 53 50 55 55 53 ≤ v < 58 50 60 60 58 ≤ v < 63 50 60 65 63 ≤ v < 68 50 60 70 v ≥ 68 50 60 70

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

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

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

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

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)

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

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_lrd_47. pdf • NCHRP Legal Research Digest 47: Judicial Enforcement of Variable Speed http: //safety. fhwa. dot. gov/fourthlevel/pdf/poynton 1. 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)

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