ROAD TRAFFIC CONSIDERED AS A RANDOM SERIES

A LARGE VOLUME OF EVIDENCE IS PRESENTED SHOWING THAT, UNDER NORMAL CONDITIONS, FREELY-FLOWING TRAFFIC CORRESPONDS VERY CLOSELY TO A RANDOM SERIES OF EVENTS. A SERIES OF EVENTS IS DEFINED AS RANDOM WHEN: (1) EACH EVENT, FOR EXAMPLE, THE MOMENT OF ARRIVAL OF A VEHICLE AT A GIVEN POINT, IS COMPLETELY INDEPENDENT OF ANY OTHER EVENT, AND (2) EQUAL INTERVALS OF TIME ARE EQUALLY LIKELY TO CONTAIN EQUAL NUMBERS OF EVENTS. SIMILAR CONDITIONS, EXPRESSED IN TERMS OF SPACE INSTEAD OF TIME, DEFINE A RANDOM DISTRIBUTION. SOME CONDITIONS ARE DISCUSSED, UNDER WHICH THE TRAFFIC DISTRIBUTION DIFFERS FROM THAT OF A RANDOM SERIES. FREELY- FLOWING TRAFFIC IS FOUND TO CONFORM SO WELL TO THE DISTRIBUTION GIVEN BY A RANDOM SERIES THAT THE LATTER MAY BE DESCRIBED AS NORMAL. DEPARTURES FROM NORMAL DISTRIBUTION ARE PRODUCED BY DISTURBANCE OF THE FREE AND UNIFORM FLOW OF TRAFFIC BY ONE OR MORE OF THE FOLLOWING CAUSES: (1) SUDDEN INCREASE OR DECREASE IN THE TRAFFIC USING THE ROAD, (2) CONTROL BY POLICE OR TRAFFIC SIGNALS AT AN ADJACENT SITE, (3) DIFFICULTY IN PASSING OTHER VEHICLES FREELY, OWING TO NARROW ROADS, TRAMWAYS, SHARP BENDS, ETC., AND (4) SATURATION, WHICH, HOWEVER, IS IN PRACTICE A RARE CONDITION. THESE ARE THE ONLY DISTURBING INFLUENCES SHOWN BY THE TRAFFIC OBSERVATIONS SO FAR AVAILABLE. SATURATION OF TRAFFIC FLOW PRODUCES VERY DIFFERENT EFFECTS. TRAFFIC FLOW IN STREETS IS VERY RARELY SATURATED, SINCE THE AMOUNT OF TRAFFIC WHICH A GIVEN STREET CAN CARRY IS USUALLY LIMITED BY A BAD DESIGN OF JUNCTIONS OR THE EFFECT OF CONTROL RATHER THAN BY THE WIDTH OF THE STREET ITSELF. IT IS CONCLUDED THAT ROAD TRAFFIC NORMALLY CONFORMS TO THE LAWS TRUE OF RANDOM SERIES, AND MAY THEREFORE BE ASSUMED TO FORM A RANDOM SERIES. THE LAWS OF RANDOM SERIES MAY BE APPLIED TO ROAD- TRAFFIC QUESTIONS IN ORDER TO OBTAIN NUMERICAL ANSWERS TO SPECIFIC TRAFFIC PROBLEMS, OR TO DECIDE QUESTIONS OF GENERAL PRINCIPLE. THE RESULTS CALCULATED FROM THESE LAWS ARE TRUE OF NORMAL TRAFFIC, BUT ARE ONLY A ROUGH APPROXIMATION FOR TRAFFIC CONDITIONS DISTURBED BY VARIABLE TRAFFIC FLOW, CONTROL, DIFFICULTY OF PASSING, OR SATURATION.

• Supplemental Notes:
  • Vol 4, pp 121-130
• Authors:
  • Adams, W F
• Publication Date: 0

Media Info

• Serial:
  • Institution Civil Engineers J /UK/
  • Issue Number: 0

Subject/Index Terms

• TRT Terms: Highway capacity; Mathematical analysis; Physical distribution; Random sampling; Traffic control; Traffic flow; Traffic flow theory; Traffic signals; Travel patterns
• Uncontrolled Terms: Traffic patterns
• Old TRIS Terms: Random series
• Subject Areas: Freight Transportation; Highways; Operations and Traffic Management;

Filing Info

• Accession Number: 00227100
• Record Type: Publication
• Files: TRIS
• Created Date: Aug 13 2004 6:56PM