PULL-IN AND DROP-OUT DELAY UNIT FOR VEHICLE DETECTOR IN TRAFFIC-CONTROL SYSTEM

• US 3,693,144 A
• Filed: 10/21/1970
• Issued: 09/19/1972
• Est. Priority Date: 10/21/1970
• Status: Expired due to Term

• Current Assignee: Milton Friedman
• Original Assignee: Milton Friedman
• Inventors: Friedman, Milton
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): Myers, Randall P.
• Application Number:
  US05/082,634
• Time in Patent Office: 699 Days
• Field of Search: 340/36,37,38R,38L
• US Class Current: 340/917
• CPC Class Codes: G08G 1/08 according to detected number or speed of vehicles
• CPC Class Codes: G08G 1/087 Override of traffic control, e.g. by signal transmitted by an emergency vehicle

Abstract

A pull-in and drop-out delay unit for a vehicle detector acting in conjunction with a traffic-light controller installed at a traffic intersection. The detector serves to sense the presence or absence of a vehicle in a zone adjacent the traffic intersection. When the detector senses the presence of a vehicle, the delay unit serves to defer the transfer of the presence signal to the traffic controller for an adjustable period to permit right-turn on '"'"''"'"''"'"''"'"'red.'"'"''"'"''"'"''"'"' When the detector senses the absence of a vehicle, the delay unit defers the transfer of the absence signal to the controller for an adjustable period whereby '"'"''"'"''"'"''"'"'tailgating'"'"''"'"''"'"''"'"' is minimized and slow-reacting vehicles are more easily passed.

Claims

1. A traffic-control system comprising A. a traffic-controller adapted to operate green and red signals at an intersection of two streets, B. detection means to sense the presence of a vehicle in a zone disposed in one of said streets to produce a call indication when a vehicle is present in said zone and a no-call indication when no vehicle is present, and C. a delay unit coupling said detection means To said controller and responsive to said indications, said unit including first means to defer the transfer of the call indication to said controller for an adjustable period to permit a sensed vehicle to make a right turn on a red signal, and second means independent of the first means to defer the transfer of a nocall indication to said controller for an adjustable period to maintain a green signal after a first vehicle has departed the zone and a second vehicle spaced from said first vehicle advances toward said zone.

2. A system as set forth in claim 1, wherein said detection means includes an inductive loop buried below said street.

3. A system as set forth in claim 1, wherein said unit includes a flip-flop circuit constituted by two cross-coupled main transistors, an output relay connected in the collector circuit of one of said transistors and having a normally-closed switch coupled to said controller to produce a green signal when the relay is de-energized, and first and second control means coupled to said first and second main transistors and incorporating an adjustable delay network, said first control means being responsive to a no-call indication to render said first transistor non-conductive after a delay period to cause said switch to open and to cause said controller to produce a red signal, said second control means being responsive to a call indication to render said second transistor non-conductive after a delay period, thereby to render said first transistor conductive to cause said switch to open to produce a red signal.

4. A system as set forth in claim 3, wherein each control means is constituted by a unijunction transistor having a charging capacitor in the emitter circuit thereof which, when the capacitor attains a given charge, fires the unijunction transistor to produce a pulse rendering the associated main transistor non-conductive.