Variable Speed Limits Speed Management Workshop Dallas TX
Variable Speed Limits Speed Management Workshop Dallas, TX March 6, 2000 Davey Warren Office of Safety R&D Federal Highway Administration
This Presentation • background • objectives • examples – foreign – domestic • lessons learned
Part-time Speed Limits 1950 2000
First variable speed system in US Michigan (1960) • Lodge Freeway • 21 speed signs over 3 mi • 60 -20 mi/h • video surveillance • gradually slow approaching backups
Variable Speed Limit Systems • traffic and speed detectors • environmental sensors • variable message signs • display safe speeds for different road conditions
Objectives • Increased 8 Relative Risk • greater safety • efficient use of 6 compliance highway facilities • less burned justice system ACCIDENT INVOLVEMENT 4 2 OVERTAKINGS 0 -20 -10 0 10 20 Deviation from mean speed, mph
European Examples • Netherlands • Germany • Finland • England
Germany • fully automated autobahns rural • variable speed signs 1 mi spacing • 130 -60 km/h per Road Traffic Code • monitor traffic, speed, surface, wind, fog • 20 -30% reduction in accident rates
German Automated Speed Control Algorithm *Unrestricted at very light traffic flow
Finland • 15 mi rural freeway • 120 -100 -80 km/h • variable speed signs – 1 mi spacing – both sides of road • hazard warning • monitor surface and weather conditions • unmanned
M 25 Motorway (UK) • automated • 70 -60 -50 mph • fog, , , Ø • fibre optic technology • “failsafe”
M 25 Enforcement System • radar speed measurement • automatic camera • rear of gantries • fixed signing • police control (civilian staff) • fine & penalty points Variable speed limit
Traffic Monitoring • speed limits obeyed • more even headways • more even lane use • less lane changing • more comfortable • minor improvements in throughput, travel times, safety, emission
US Examples • NJ Turnpike • Tennessee • Washington • New Mexico
New Jersey Turnpike • 120 signs over 148 miles • 65 -30 mi/h • based on mean speed • north section automated • hazard warning signs
Tennessee (I-75) • Fog warning • Speed and visibility sensors • Microwave link to police center • Semi-automated Photo courtesy of PB Farradyne
Washington (I-90) • 17 mi over mountain pass • monitor speed, road surface and weather • 65 -35 mi/h during winter • hazard warning • semi-automated
Photo courtesy of PB Farradyne
New Mexico (I-40) • fully automated • maximum speed • minimum speed or hazard warning
Prototype test constrained by NMSL
Maximum and Minimum Limit
Downstream Hazard Warning
Roadside station downstream of each interchange
Central station (unmanned) • communication hub • permanent log of speed limits • monitor system status remotely • manual over-ride
New Mexico Automated Speed Control Algorithm
Smooth Mean Speed
System Performance
Lessons • Sign location, spacing and visibility • Power failure • Control algorithm – Smooth speed – Hysteresis – max & min • Environmental sensing • Low cost & fully autonomous
Questions Davey Warren FHWA HRDS-05 6300 Georgetown Pike Mc. Lean, VA 22101 -2296 202 -493 -3318 davey. warren@fhwa. dot. gov
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