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

Part-time Speed LimitsPart-time Speed Limits

19501950 20002000

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

Photo courtesy of PB Farradyne

New Mexico (I-40)New Mexico (I-40)

•fully automatedfully automated

•maximum speedmaximum speed

•minimum speed or minimum speed or hazard warninghazard warning

Prototype test constrained by NMSLPrototype test constrained by NMSL

Maximum and Minimum LimitMaximum and Minimum Limit

Downstream Hazard WarningDownstream Hazard Warning

Roadside station downstream Roadside station downstream of each interchangeof each interchange

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

System PerformanceSystem Performance

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

davey.warren@fhwa.dot.gov