Variable Speed Limits Making Work Zones Work Better Workshop Orlando, Florida 17 Sept. 03 Davey...
-
Upload
suzanna-henderson -
Category
Documents
-
view
216 -
download
2
Transcript of Variable Speed Limits Making Work Zones Work Better Workshop Orlando, Florida 17 Sept. 03 Davey...
Variable Speed Limits
Making Work Zones Work Better Workshop Orlando, Florida 17 Sept. 03
Davey WarrenOffice of Safety ProgramsFederal 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
Focus of presentation
• Modern systems change the speed limits in real time:• Traffic conditions
• Adverse weather conditions
• Road surface conditions
• Work Zones
19601960
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?
0
10
20
30
40
50
60
70
80
0 2 4 6 8 10 12 14 16 18 20 22 24TIME
Spe
ed,
mi/h
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
20
30
40
50
60
70
80
0 2 4 6 8 10 12 14 16 18 20 22 24
TIME
Sp
ee
d,
mi/h
Smooth speed Speed Limit Speed Limit With Histeresis
Average Speeds and Variable Limit Over 24 hr
Congestion
• Examples
Lodge Freeway, MI
M25, UK
Netherlands
• Characteristics• Cover stretches of congested roadways
• Speeds set to reflect traffic conditions
• Slow traffic approaching backups
19601960
Winter Weather and Road Conditions
• ExamplesI-90, Washington
E18, Finland
I-40, Arizona
• Characteristics• Cover longer stretches of weather-susceptible
roadways
• Speeds set to reflect roadway/weather/visibility conditions
Fog
• ExamplesI-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 29k – 53k
• (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 Unprotected
2 Workers Present
3 No Work Activity
L.O. Threshold - 0% 50 60 70
H.O. Threshold – 70% 40 40 40
v < 40 40 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 Informationhttp://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)
Questions
Davey Warren
FHWA HSA-20
400 7th Street, SW
Washington, DC 20590
202-366-4668