HIGH SPEED SIGNAL DESIGN

A DIFFICULTY THAT BESETS EXISTING TRAFFIC-ACTUATED CONTROL SYSTEMS IS THAT TRAFFIC DYNAMICS MAKE IT IMPOSSIBLE TO EXTRAPOLATE FROM TIME DELAYS TO SPATIAL GAPS, SINCE ACCELERATION AND CAR FOLLOWING MAY OCCUR IN THE INTERVAL BETWEEN REGISTRATION OF AN ACTUATING TIME GAP AND THE SIGNAL CHANGE FROM GREEN TO AMBER. A CONCEPT CALLED "AREA DETECTION" IS PROPOSED TO OVERCOME THIS SHORTCOMING. A SERIES OF LOOP DETECTORS WITH TIME DELAYS IS USED TO MEASURE SPACE GAPS INSTEAD OF TIME GAPS. IN "NORMAL" TRAFFIC ANY CAR WITHIN 300 FEET OF AN INTERSECTION WILL GO THROUGH ON THE GREEN; IT IS ASSUMED THAT AN AMBER WARNING AT A DISTANCE OF 300 FEET OR MORE WILL INDUCE THE DRIVER TO PREPARE TO STOP. A 60-FOOT LOOP DETECTOR COVERS THE FIRST 60 FEET FROM THE STOP BAR, AND A SECONDARY ZONE OF DETECTORS COVERS DISTANCES OUT TO 800 FEET UNLESS THEY ARE DISCONNECTED LBY A VOLUME-LEVEL INDICATOR. THE OPERATION OF THE DETECTORS IN LIGHT AND HEAVY TRAFFIC IS DESCRIBED, TOGETHER WITH VARIABLE OPERATING MODES INDUCED BY TRAFFIC CONDITIONS. TWO INSTALLATIONS IN SAN DIEGO HAVE GREATLY REDUCED RIGHT-OF-WAY ACCIDENTS OVER THE PAST TWO YEARS. THE DRAWBACKS OF THE SYSTEMS ARE FINANCIAL: ADDITIONAL DETECTORS USUALLY RUN $4--10 THOUSAND DOLLARS MORE THAN CONVENTIONAL SIGNALS, MAINTENANCE LABOR IS ABOUT DOUBLED, AND THE OVERALL COST INCREASE IS ABOUT 65%. HOWEVER, AN ACCIDENT-COST ANALYSIS OF THE TWO SAN DIEGO INTERSECTIONS INDICATED THAT THE NEW DETECTORS HAD SAVED ABOUT $67,000.

• Supplemental Notes:
  • Vol 35, No 6, PP 8-10, 3 FIG
• Authors:
  • MATTHEWS, R
  • Schowengerdt, L N
• Publication Date: 1970-11

Media Info

• Serial:
  • Public Safety Systems

Subject/Index Terms

• TRT Terms: Building; Costs; Distance; Distance measuring equipment; Facilities; Installation; Intersections; Loop detectors; Loops (Control systems); Magnetometers; Maintenance management; Rear end crashes; Speed; Stochastic processes; Stopping distances; Traffic; Traffic actuated controllers; Traffic control; Traffic volume; Vehicle detectors
• Uncontrolled Terms: Maintenance costs
• Old TRIS Terms: Loops (Electrical)
• Subject Areas: Construction; Data and Information Technology; Finance; Highways; Maintenance and Preservation; Operations and Traffic Management;

Filing Info

• Accession Number: 00225919
• Record Type: Publication
• Files: TRIS
• Created Date: May 16 1971 12:00AM