Showing papers in "Highway Research Board Special Report in 1964"

On kinetic waves, II . A theory of traffic flow on long crowded roads

Abstract: This paper uses the method of kinematic waves, developed in part I, but may be read independently. A functional relationship between flow and concentration for traffic on crowded arterial roads has been postulated for some time, and has experimental backing (§2). From this a theory of the propagation of changes in traffic distribution along these roads may be deduced (§§2, 3). The theory is applied (§4) to the problem of estimating how a ‘hump’, or region of increased concentration, will move along a crowded main road. It is suggested that it will move slightly slower than the mean vehicle speed, and that vehicles passing through it will have to reduce speed rather suddenly (at a ‘shock wave’) on entering it, but can increase speed again only very gradually as they leave it. The hump gradually spreads out along the road, and the time scale of this process is estimated. The behaviour of such a hump on entering a bottleneck, which is too narrow to admit the increased flow, is studied (§5), and methods are obtained for estimating the extent and duration of the resulting hold-up. The theory is applicable principally to traffic behaviour over a long stretch of road, but the paper concludes (§6) with a discussion of its relevance to problems of flow near junctions, including a discussion of the starting flow at a controlled junction. In the introductory sections 1 and 2, we have included some elementary material on the quantitative study of traffic flow for the benefit of scientific readers unfamiliar with the subject.

Simulation of traffic flow

Abstract: SIMULATION OF VEHICULAR TRAFFIC ON HIGH-SPEED COMPUTERS IS A TECHNIQUE WHICH ENABLES THE STUDY OF A COMPLEX TRAFFIC SYSTEM IN THE LABORATORY RATHER THAN IN THE FIELD. THE USE OF COMPUTERS IS DESCRIBED USING ANALOGUE AND DIGITAL SIMULATION. IN ANALOGUE SIMULATION, THE MATHEMATICAL MODELS USED MUST BE THOSE WHICH INVOLVE DIFFERENTIAL EQUATIONS OR WHICH CAN BE MADE TO LOOK AS THOUGH THEY INVOLVED DIFFERENTIAL EQUATIONS. WITH DIGITAL SIMULATION, HOWEVER, IT IS POSSIBLE TO USE MODELS DESCRIBED IN WORDS RATHER THAN MATHEMATICAL TERMS. TECHNIQUES OF MODEL FORMULATION AND BLOCK DIAGRAMS ARE DESCRIBED WHICH ARE USED IN THE SIMULATION OF ANY SYSTEM. MATHEMATICAL TECHNIQUES USED ARE DISCUSSED. PROBABILITY DISTRIBUTIONS OF TRAFFIC INPUT CHARACTERISTICS, MONTE CARLO METHODS, AND POISSON DISTRIBUTION. EXAMPLES PRESENTED ARE OF: INTERSECTION, FREEWAY TRAFFIC FLOW AND TRAFFIC STUDIES. PUBLISHED SIMULATION WORK ON STUDIES OF TRAFFIC FLOW WERE MADE ON THE FOLLOWING TYPES OF FACILITIES: SIGNALIZED STREETS, FREEWAYS, AND TUNNELS.

Car following and acceleration noise

Abstract: THE AVERAGE SPEED OR TRAVEL TIME FOR A SMOOTH SAFE DRIVING ON A GIVEN ROAD DEPENDS ON MANY PHENONMENA. TWO FACTORS DETERMINE THE MAINTENANCE OF A SMOOTH SAFE TRIP: THE MOTION OF AN ISOLATED VEHICLE, AND THE INTERFERENCE OF VEHICLES WITH EACH OTHER. THE ACCELERATION PATTERN OF AN ISOLATED VEHICLE, AS A FUNCTION OF TIME, HAS A RANDOM APPEARANCE CALLED ACCELERATION NOISE. A MATHEMATICAL EQUATION IS DESIRED TO EXPRESS ACCELERATION NOISE OF DISPERSION. METHODS OF MEASURING ACCELERATION NOISE ARE DESCRIBED. EQUATIONS ARE DERIVED TO EXPRESS THE LAW OF CAR FOLLOWING IN VARIATION OF FLOW WITH DENSITY. THE EFFECT OF DISTURBANCES AND OF STABILITY OF LINEAR SYSTEMS IS FREQUENTLY INVESTIGATED BY MAKING HARMONIC (FREQUENCY) ANALYSIS OF THE DISTURBANCE TO SEE HOW INDIVIDUAL FREQUENCY COMPONENTS ARE PROPAGATED THROUGH THE SYSTEM. THE HARMONIC ANALYSIS IS MADE AND COMPARED WITH EXPERIMENTAL DATA. HAVING ANALYZED ACCELERATION NOISE OF AN ISOLATED VEHICLE AND SEVERAL SIMPLE CAR-FOLLOWING LAWS FOR TRAFFIC, IT IS ASSUMED THAT THE TOTAL ACCELERATION NOISE OF A VEHICLE IN TRAFFIC IS A SUPERPOSITION OF ITS NATURAL NOISE AND ITS RESPONSE TO THAT OF ITS PREDECESSORS THROUGH THE LAW OF FOLLOWING. ANALYSIS BY HERMAN AND ROTHERY INDICATE THAT TRAFFIC BROADENS THE ACCELERATION DISTRIBUTION FUNCTION SO THAT THE DISPERSION FAR DOWN THE PLATOON IS ABOUT THREE TIMES THAT OF THE LEAD CAR, WHICH IS EFFECTIVELY MOVING FREELY ON THE ROAD. THE BROADENING OF THE ACCELERATION DISTRIBUTION BY TRAFFIC DEPENDS ON THE PARAMETERS OF THE LAW OF FOLLOWING. AN EQUATION IS DERIVED TO EXPRESS THESE VALUES.

A critical review of literature treating methods of identifying aggregates subject to destructive volume change when frozen in concrete and a proposed program of research

Abstract: CONTENTS' FREEZING-AND-THAWING EFFECTS, HISTORY, AND CURRENT THEORY BUILDING STONE AND BRICK CONCRETE AND MORTAR AGGREGATES RESEARCH ON METHODS FOR IDENTIFYING FROST-SUSCEPTIBLE AGGREGATES SOUNDNESS TESTS PETROGRAPHIC ANALYSIS PORE SYSTEM STUDIES PHYSIO-CHEMICAL PROPERTIES STUDIES FREEZING-AND-THAWING TESTS MISCELLANEOUS POSSIBLE APPROACHES SUMMARY AND RECOMMENDED AREAS FOR RESEARCH ANNOTATED BIBLIOGRAPHY /BY ABOVE SECTIONS/

Queueing theory approaches

Abstract: RESULTS ARE PRESENTED OF SOME OF THE STUDIES OF PROBABILITY MODELS OF TRAFFIC DELAY. SOME FUNDAMENTAL CHARACTERISTICS ARE DESCRIBED OF VARIABLE PROCESSES AS WELL AS THE IMPORTANT ASSUMPTIONS GOVERNING THE ARRIVAL OF STREAMS OF TRAFFIC AT A GIVEN POINT AND THE VARIABILITY OF GAP ACCEPTANCE OF DRIVERS AND PEDESTRIANS ATTEMPTING TO CROSS A TRAFFIC STREAM. A BRIEF SUMMARY IS PRESENTED OF SOME ELEMENTS OF QUEUEING OR WAITING-LINE THEORY FROM THE BRANCH OF MATHEMATICS DEALING WITH CONGESTED SYSTEMS. SUMMARIES ARE PRESENTED OF THE MOST SIGNIFICANT PUBLISHED WORKS RELATIVE TO DELAYS AT SIGNALIZED AND STOP-SIGN CONTROLLED INTERSECTIONS, PASSING ON A TWO-LANE ROADWAY, AND A NUMBER OF SPECIAL TOPICS SUCH AS MULTIPLE QUEUES, PARKING AND ONE-LANE BOTTLENECKS.

Some experiments and applications

Abstract: FACTORS WHICH TEND TO LIMIT THE USE OF TRAFFIC EXPERIMENTATION FOR SCIENTIFIC PURPOSES ARE: (1) THE INACCESSIBILITY OF EXPERIMENTAL SITUATIONS FOR MOST TRAFFIC THEORISTS, (2) THE EXPENSE OF INSTRUMENTATION FOR TRAFFIC EXPERIMENTS, AND (3) THE TIME USUALLY NEEDED TO REDUCE DATA FOR ANALYSIS. IMPORTANT GAINS ARE BEING MADE TO MEET THESE NEEDS. THERE HAS BEEN CONSIDERABLE PROGRESS IN THE DEVELOPMENT OF TRAFFIC INSTRUMENTATION SYSTEMS FOR MEASURING DRIVER BEHAVIOR AND VEHICULAR MOVEMENT. THE FOLLOWING TECHNIQUES ARE DISCUSSED WHICH HAVE BECOME ESSENTIAL IN THE STUDY OF COMPLEX TRAFFIC FLOW PROBLEMS: PHOTOGRAPHIC, CAR FOLLOWING, TRANSDUCERS, RECORDS, AND COMPUTERS. THCHNIQUES USED IN STUDYING DRIVER BEHAVIOR ARE: FORBES' MEASUREMENTS OF DRIVER REACTION TIME, DRIVING SIMULATION, AND GALVANIC SKIN REFLEX STUDIES. THE THEORY OF CAR FOLLOWING DESCRIBES THE MANNER IN WHICH ONE VEHICLE FOLLOWS ANOTHER. DATA WERE DERIVED FROM THE FOLLOWING EXPERIMENTS WHICH SUBSTANTIATED THE THEORY: FORBES' TUNNEL EXPERIMENTS AND GENERAL MOTORS CAR-FOLLOWING EXPERIMENTS. TRAFFIC BEHAVIOR WITHIN PLATOONS WAS STUDIED BY: FORBES' PLATOON STUDIES IN PASADENA, PORT AUTHORITY PLATOON EXPERIMENTS AND PLATOON FLOW THROUGH INTERSECTION TRAFFIC SIGNAL SYSTEMS. STUDIES ON THE CHARACTERISTICS OF TRAFFIC FLOW COMPARED TO WATER FLOW WERE MADE BY GREONSHIELDS, SPEED HEADWAY MEASURES BY ALCOTT OIL, EXPERIMENTS IN THE NEW YORK TUNNELS USING FLUID FLOW MODELS, AND EXPERIMENTAL WORK BY EDEDIE, FOOT, HERMAN AND ROTHERY. TRAFFIC THEORY OF FLOW CONTROL EXPERIMENTS LOCATE BOTTLE NECKS AND MEASURE TRAFFIC CAPACITY: (1) MANUAL TRAFFIC SPACING EXPERIMENTS OF GREENBERG AND DAOU, (2) INSTRUMENTED TRAFFIC SPACING BY FOOT, CROWLEY AND GONSETH, (3) EXPERIMENTS WITH COMPLETELY AUTOMATIC FLOW CONTROL SYSTEM, (4) TRAFFIC SURVEILLANCE ON THE JOHN LODGE EXPRESSWAY IN DETROIT, AND (5) CONGRESS FLOW CONTROL USED IN NEW YORK INCREASES THE PROPORTION OF TIME THAT TRAFFIC PASSES OVER A CRITICAL ROADWAY, KEEPING IT THAT TRAFFIC PASSES OVER A CRITICAL ROADWAY BY KEEPING IT MOVING SMOOTHLY AT MID-RANGE SPEEDS. OTHER EXPERIMENTS CONDUCTED TO DETERMINE IF TRAFFIC FLOW THROUGH A SERIES OF INTERSECTIONS CAN BE INCREASED BY CONTROLLING THE SPACING OF VEHICLES ENTERING THE CRITICAL AREA WERE: (1) DUSSELDORF'S SIGNAL FUNNEL, (2) EXPERIMENTS WITH PACER SYSTEM IN DETROIT, AND (3) TRAFFIC SIGNAL CONTROL EXPERIMENTS IN TORONTO.