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Variable Speed LimitsVariable Speed Limits
Speed Management Workshop Dallas, TXMarch 6, 2000
Davey Warren Davey Warren Office of Safety R&DOffice of Safety R&DFederal Highway AdministrationFederal Highway Administration
This PresentationThis Presentation
• backgroundbackground
• objectivesobjectives
• examplesexamples– foreignforeign– domesticdomestic
• lessons learnedlessons learned
First variable speed system in USFirst variable speed system in USMichigan (1960)Michigan (1960)
• Lodge FreewayLodge Freeway
• 21 speed signs 21 speed signs over 3 miover 3 mi
• 60-20 mi/h60-20 mi/h
• video video surveillancesurveillance
• gradually slow gradually slow approaching approaching backupsbackups
Variable Speed Limit SystemsVariable Speed Limit Systems
• traffic and speed traffic and speed detectorsdetectors
• environmental sensorsenvironmental sensors
• variable message signsvariable message signs
• display safe speeds for display safe speeds for different road conditionsdifferent road conditions
ObjectivesObjectives
• Increased Increased compliancecompliance
• greater safetygreater safety
• efficient use of efficient use of highway highway facilitiesfacilities
• less burned less burned justice systemjustice system
0
2
4
6
8
0 10 20-10-20
Relative Risk
Deviation from mean speed, mph
OVERTAKINGS
ACCIDENTINVOLVEMENT
European ExamplesEuropean Examples
• NetherlandsNetherlands
• GermanyGermany
• FinlandFinland
• EnglandEngland
GermanyGermany
• fully automated rural fully automated rural autobahnsautobahns
• variable speed signs 1 mi variable speed signs 1 mi spacingspacing
• 130-60 km/h per 130-60 km/h per Road Traffic CodeRoad Traffic Code
• monitor traffic, speed, monitor traffic, speed, surface, wind, fogsurface, wind, fog
• 20-30% reduction in 20-30% reduction in accident ratesaccident rates
German Automated Speed German Automated Speed Control AlgorithmControl Algorithm
TrafficFlow
DayDry
DarkDry
DayWet
DarkWet Extreme
Low 130* 120 110 110 90..60
Mod 110 110 100 100 90..60
High 90 90 80 80 90..60
Unstable 70 70 70 70 60
*Unrestricted at very light traffic flow
FinlandFinland
• 15 mi rural freeway15 mi rural freeway
• 120-100-80 km/h120-100-80 km/h
• variable speed signsvariable speed signs– 1 mi spacing1 mi spacing– both sides of roadboth sides of road
• hazard warninghazard warning
• monitor surface and monitor surface and weather conditionsweather conditions
• unmanned unmanned
M25 Motorway (UK)M25 Motorway (UK)
• automated automated
• 70-60-50 mph70-60-50 mph
• fog,fog,, , , Ø, Ø
• fibre optic fibre optic
technologytechnology
• ““failsafe” failsafe”
M25 Enforcement SystemM25 Enforcement System
• radar speed measurementradar speed measurement
• automatic cameraautomatic camera
• rear of gantriesrear of gantries
• fixed signingfixed signing
• police control (civilian police control (civilian staff)staff)
• fine & penalty pointsfine & penalty points
Variablespeedlimit
Traffic MonitoringTraffic Monitoring
• speed limits obeyedspeed limits obeyed
• more even headwaysmore even headways
• more even lane usemore even lane use
• less lane changingless lane changing
• more comfortablemore comfortable
• minor improvements in throughput, travel times, minor improvements in throughput, travel times,
safety, emissionsafety, emission
US ExamplesUS Examples
• NJ TurnpikeNJ Turnpike
• TennesseeTennessee
• WashingtonWashington
• New MexicoNew Mexico
New Jersey TurnpikeNew Jersey Turnpike
• 120 signs over 148 120 signs over 148 milesmiles
• 65-30 mi/h65-30 mi/h
• based on mean based on mean speedspeed
• north section north section automatedautomated
• hazard warning hazard warning signssigns
Tennessee (I-75)Tennessee (I-75)
• Fog warningFog warning
• Speed and Speed and visibility sensorsvisibility sensors
• Microwave link Microwave link to police centerto police center
• Semi-automatedSemi-automated
Photo courtesy of PB Farradyne
Washington (I-90)Washington (I-90)
• 17 mi over 17 mi over mountain passmountain pass
• monitor speed, monitor speed, road surface and road surface and weatherweather
• 65-35 mi/h during 65-35 mi/h during winterwinter
• hazard warninghazard warning
• semi-automatedsemi-automated
New Mexico (I-40)New Mexico (I-40)
•fully automatedfully automated
•maximum speedmaximum speed
•minimum speed or minimum speed or hazard warninghazard warning
Central station (unmanned)Central station (unmanned)
• communication communication hubhub
• permanent log of permanent log of speed limitsspeed limits
• monitor system monitor system status remotelystatus remotely
• manual over-ridemanual over-ride
New Mexico Automated Speed New Mexico Automated Speed Control AlgorithmControl Algorithm
Smooth Mean Speed +/-Max
(mi/h)Min
(mi/h)Max
(std. dev.)Min
(std. dev.)
Dry Day + 6.5 - 6.0 1.0 -1
Dry Dark + 5.0 - 5.0 .75 -.75
Wet Day + 2.5 na .5 na
Wet Dark + 0 na 0 na
Smooth Mean SpeedSmooth Mean Speed
0
10
20
30
40
50
60
70
80
0 2 4 6 8 10 12 14 16 18 20 22 24
TIME
mi/h
Lessons Lessons
• Sign location, spacing and Sign location, spacing and visibilityvisibility
• Power failurePower failure
• Control algorithmControl algorithm– Smooth speedSmooth speed
– HysteresisHysteresis
– max & minmax & min
• Environmental sensingEnvironmental sensing
• Low cost & fully autonomousLow cost & fully autonomous
QuestionsQuestions
Davey WarrenDavey Warren
FHWA HRDS-05FHWA HRDS-05
6300 Georgetown Pike6300 Georgetown Pike
McLean, VA 22101-2296McLean, VA 22101-2296
202-493-3318202-493-3318