DETECTOR PLACEMENT - A MISUNDERSTOOD SUBJECT

FOR EFFICIENT OPERATION, DETECTOR PLACEMENT MUST TAKE INTO CONSIDERATION THE AVERAGE TIME OF THE ARRIVING VEHICLES AND THE TOLERABLE TIME SEPARATION BETWEEN VEHICLES WHICH WILL BE PERMITTED TO HOLD THE GREEN SIGNAL. THIS TIME SPACING MUST BE DETERMINED BY THE ENGINEER AND SHOULD BE BASED ON THE NATURE OF TRAFFIC FLOW AT THE PARTICULAR INTERSECTION. WITH SIMPLE FLUCTUATED EQUIPMENT THE ALLOWABLE HEADWAY TO HOLD THE GREEN IS USUALLY AT LEAST 3 SECONDS. LONGER HEADWAYS ARE SOMETIMES FOUND TO BE OPERATIONALLY MORE ACCEPTABLE. USING A 25-MPH APPROACH SPEED AND A 4-SECOND HEADWAY, ONE HUNDRED AND THIRTY FEET HAS BEEN CALCULATED AS THE DISTANCE THAT THE DETECTOR (ASSUMING IT IS A PRESENCE DEVICE BUT HAS IN ITSELF NO LONGITUDINAL DIMENSION ALONG THE ROADWAY) SHOULD BE PLACED FROM THE STOP LINE, IF THE VEHICLES ARE TO HOLD THE GREEN SIGNAL. THE LOOP-DETECTOR AND ITS USE IS DESCRIBED. TRAFFIC ENGINEER OPINION THAT DETECTOR PLACEMENT 125 FT FROM THE STOP LINE REQUIRES TOO LONG AN INITIAL PERIOD IN THE CONTROLLER SYSTEM IS DISCUSSED. THE PROBLEMS OF UNDETECTED VEHICLE APPROACH AND THE INCREASE IN REAR-END COLLISIONS ESPECIALLY AT SEMIACTUATED INTERSECTIONS ARE CONSIDERED AND REMEDIAL MEASURES ARE RECOMMENDED. IN THE DISCUSSION OF SEMIACTUATED CONTROLLERS, IT IS ASSUMED THAT IT WILL BE USED ONLY WITH COORDINATED OPERATION ON THE MAJOR OR NON-ACTUATED ROAD. THE DIFFERENCE IN DETECTOR LOCATIONS IN THE TWO DIFFERENT TYPES OF CONTROLLERS IS IMPORTANT. WITH THE FULL ACTUATED CONTROLLER, THE EMPHASIS IS ON SAFE, EFFICIENT OPERATION OF ALL VEHICLES FROM HEAVY TRAFFIC PERIODS TO THE LIGHTEST OFF-PEAK PERIODS. WITH SEMIACTUATED CONTROL EQUIPMENT, THE EMPHASIS IS ON CONTINUED MOVEMENT OF TRAFFIC ON THE MAJOR STREET WITH THE ACTUATED MINOR STREET TAKING DELAYS TO VEHICLES. DETECTOR PLACEMENT FOR THE MORE SOPHISTICATED VOLUME DENSITY CONTROLLER MAY BE AT A MUCH GREATER DISTANCE FROM THE STOP LINE. VOLUME DENSITY CONTROLLERS MAXIMIZE EFFICIENCY OF THE INTERSECTION BY MAKING BETTER USE OF THE TOTAL AVAILABLE GREEN PERIODS. MEANS ARE ALSO PROVIDED TO AVOID LONG INITIAL PERIODS WHEN ONLY A FEW CARS ARE WAITING.

• Authors:
  • Rodgers, L M
• Publication Date: 1973-4

Media Info

• Features: Figures; References;
• Pagination: p. 42-4
• Serial:
  • Traffic Engineering, Inst Traffic Engr
  • Volume: 43
  • Issue Number: 7

Subject/Index Terms

• TRT Terms: Actuated traffic signal controllers; Full traffic actuated controllers; Semi traffic actuated controllers; Traffic actuated controllers; Traffic control devices; Volume
• Old TRIS Terms: Semiactuated traffic signal controller
• Subject Areas: Highways; Operations and Traffic Management;

Filing Info

• Accession Number: 00226662
• Record Type: Publication
• Files: TRIS
• Created Date: Aug 31 1973 12:00AM