ROAD TRAFFIC CALCULATIONS

CONSIDERATION IS GIVEN TO THE FLOW OF TRAFFIC AND OF DELAYS THEREIN. TRAFFIC COUNTS TAKEN AT PLACES WHERE THE TRAFFIC VOLUME IS CLEARLY AT OR VERY NEAR THE MAXIMUM WHICH THE ROAD CAN CARRY AT THAT POINT, EXHIBIT CONSIDERABLE VARIATION, EVEN WHEN ALLOWANCE IS MADE FOR WIDTH. IT IS POSSIBLE TO MEASURE SATURATION DENSITY BY COUNTING THE TRAFFIC FOR THE SHORT PERIODS DURING WHICH IT IS RUNNING AT ITS HIGHEST DENSITY. WHILE IT IS POSSIBLE TO OBSERVE THE DENSITY OF DENSE TRAFFIC-STREAMS, IT IS DIFFICULT TO MAKE OBSERVATIONS OF THE RELATION BETWEEN SPEED AND THE MAXIMUM SAFE DENSITY. CLEARLY THE MAXIMUM DENSITY IS OBTAINED WHEN THERE IS NO OVERTAKING. IF ALL OF THE VEHICLES ARE TRAVELLING AT THE SAME SPEED THE MAXIMUM NUMBER OF VEHICLES WHICH CAN PASS IN A GIVEN TIME WITH SAFETY MUST DEPEND UPON THE MINIMUM SAFE HEADWAY, AND SECOND, BETWEEN ONE VEHICLE AND THE NEXT. EQUATIONS ARE GIVEN TO CALCULATE THE MAXIMUM CAPACITY AT A SPEED OF BETWEEN 20 AND 25 MILES PER HOUR, WHICH IS USUALLY KNOWN AS THE ECONOMIC SPEED - ECONOMIC, THAT IS, FROM THE POINT OF VIEW OF THE HIGHWAY AUTHORITY, AND NOT THE MOTORIST. THE CAPACITY OF A TWO-WAY ROAD WIDE ENOUGH FOR AN ODD NUMBER OF TRAFFIC-LANES SHOULD BE TAKEN AS THAT OF THE NEXT LOWER EVEN NUMBER OF LANES, BECAUSE THE ODD LANE IS USABLE ONLY FOR OVERTAKING. IT IS DESIRABLE TO DETERMINE HOW THE MOST SUITABLE CYCLE-TIME VARIES WITH TRAFFIC-VOLUME. THE MOST EFFICIENT CYCLE IS THE SHORTEST WHICH WILL HANDLE THE TRAFFIC. EXPRESSIONS ARE GIVEN WHICH, IN ADDITION TO ENABLING A SUITABLE CYCLE FOR FIXED-CYCLE SIGNALS TO BE DETERMINED, MAY BE USED TO ESTIMATE THE AVERAGE CYCLE OF VEHICLE-OPERATED SIGNALS AND FOR POLICE CONTROL WHEN THE TRAFFIC IS HEAVY. AN APPROXIMATE FORMULA IS PRESENTED TO DETERMINE THE TOTAL CAPACITY OF AN INTERSECTION. EXPRESSIONS ARE GIVEN TO DETERMINE THE CAPACITY OF ROUNDABOUTS AND ONE-WAY STREETS, DELAY AT INTERSECTIONS, AND DETERMINE THE EFFECT OF STANDING VEHICLES UPON MOVING TRAFFIC. THE METHODS DESCRIBED CAN BE APPLIED TO THE SOLUTION OF SPECIFIC PROBLEMS IN TRAFFIC-CONTROL AND THE DESIGN OF STREET IMPROVEMENTS, OR TO THE DETERMINATION OF GENERAL PRINCIPLES. THE AUTHOR STATES THAT HIS PAPER WAS DELIBERATELY CONFINED TO THE CALCULATIONS OF TRAFFIC-FLOW PRINCIPALLY AT JUNCTIONS, BECAUSE THE JUNCTION WAS THE MOST IMPORTANT FEATURE WHEN TRAFFIC-FLOW WAS UNDER CONSIDERATION.

• Supplemental Notes:
  • Vol 16, No 7, PP 247-284 & NO 8, PP 588-594
• Authors:
  • Clayton, A J
• Publication Date: 0

Media Info

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

Subject/Index Terms

• TRT Terms: Highway capacity; Intersections; Mathematical analysis; One way traffic; Traffic actuated controllers; Traffic control; Traffic counting; Traffic delays; Traffic density; Traffic flow; Traffic speed; Traffic volume
• Uncontrolled Terms: Intersection capacity
• Subject Areas: Highways; Operations and Traffic Management;

Filing Info

• Accession Number: 00227102
• Record Type: Publication
• Files: TRIS
• Created Date: Aug 13 2004 6:56PM