DEVELOPMENT AND VALIDATION OF A DIGITAL SIMULATION MODEL FOR RESEARCH IN GEOMETRIC DESIGN AND CONTROL OF DIAMOND INTERCHANGES

A DIGITAL COMPUTER SIMULATION MODEL WAS DEVELOPED TO ALLOW THE CONTROLLED ANALYSIS OF TRAFFIC OPERATIONS IN A SIGNALIZED DIAMOND INTERCHANGE. THE MODEL HAS THE CAPABILITY OF REPRESENTING ALL THE SIGNIFICANT IDENTIFIABLE CHARACTERISTIC FEATURES OF DIAMOND INTERCHANGES AND THEIR OPERATION. THIS INCLUDES GEOMETRICS, SIGNAL CONTROL, TRAFFIC DEMANDS, AND VEHICLE-DRIVER CHARACTERISTICS. A DISTINCTIVE FEATURE OF THE MODEL IS THAT IT INTERRELATES IN ONE PACKAGE A FREEWAY, A SIGNALIZED ARTERIAL STREET AND THE CONNECTING RAMPS. VARIATIONS IN THE OPERATIONAL CHARACTERISTICS AND THE INTERFACES OF THESE DIFFERENT TYPES OF FACILITIES ARE APPROPRIATELY ACCOMMODATED IN THE MODEL, WHICH ALSO TAKES INTO EXPLICIT ACCOUNT ALL THE COMPLEX TURNING MOVEMENTS CHARACTERISTIC OF DIAMOND INTERCHANGES. TWO DIFFERENT MODELING APPROACHES WERE USED IN THE DEVELOPMENT OF THE OVERALL MODEL: THE FREEWAY AND ON-RAMP PORTION OF THE INTERCHANGE WERE MODELED MACROSCOPICALLY, WHILE THE ARTERIAL AND OFF-RAMPS PORTION WERE MODELED MICROSCOPICALLY. THIS COMBINATION SERVES TO REDUCE COMPUTER RUNNING TIME, WHILE AT THE SAME TIME DETAILED VEHICLE TRAJECTORY INFORMATION IS USED WHERE NECESSARY IN THE STUDY OF TRAFFIC CONTROL TECHNIQUES. THE SIMULATION MODEL WAS CODED IN JOVIAL FOR THE IBM SYSTEM 360/67. THE GEOMETRICS OF THE INTERCHANGE WERE SUBDIVIDED INTO MODULES WHOSE CHARACTERISTICS ARE ESSENTIALLY UNIFORM. DUMMY REGIONS ALSO WERE DEVELOPED TO SERVE AS APPROPRIATE LOADS TO APPLY AT THE DOWNSTREAM ENDS OF THE INTERCHANGE BRANCHES. COMBINATIONS OF THESE MODULES CAN BE INTERCONNECTED TO FORM A WIDE VARIETY OF DIAMOND INTERCHANGE CONFIGURATIONS. TRAFFIC INPUTS TO THE MODEL CAN BE APPLIED EITHER THROUGH A STOCHASTIC GENERATOR OR BY MEANS OF A SIMTAPE (TAPED SEQUENCE OF VEHICLES). MODEL PERFORMANCE OUTPUTS ARE MADE AVAILABLE PRINCIPALLY IN TERMS OF AVERAGE TRAVEL TIME AND VELOCITY, ALTHOUGH OTHER PERFORMANCE MEASURES, SUCH AS NUMBER OF VEHICLE-SECONDS STOPPED CAN ALSO BE MADE AVAILABLE. ALL IDENTIFIABLE KEY MODEL PARAMETERS ARE MODIFIABLE THROUGH A SPECIALLY DEVELOPED PROCEDURE, TERMED NUDATA, WHICH PERMITS EXAMINATION OF THE EFFECTS OF SEVERAL PARAMETER CHANGES ON THE MODEL DURING ONE COMPUTER RUN. SPECIAL EFFORTS WERE EXPENDED TO DEVELOP A DIAMOND INTERCHANGE MODEL THAT GENERATES REALISTIC OUTPUTS. EMPHASIS WAS PLACED ON THE TESTING AND VALIDATION OF THE MODEL. TO EXPEDITE VALIDATION, THE OVERALL MODEL WAS SUBDIVIDED INTO FOUR SUBMODELS. THE APPROACH SELECTED FOR MODEL VALIDATION WAS TO COLLECT AERIAL PHOTOGRAPHY DATA OF TRAFFIC OPERATIONS ON A SELECTED INTERCHANGE. THESE DATA ARE REDUCED BY A COMPLEX HARDWARE-SOFTWARE SYSTEM WHICH PRODUCES SIMTAPE AND A STATISTICAL SUMMARY OF THE PROCESSED VEHICULAR INFORMATION FROM THE FILM. THE SIMTAPE, WHICH IS A MAGNETIC TAPE RECORD OF THE TIME HISTORY OF KEY VEHICLE CHARACTERISTICS, IS USED TO CALIBRATE AND VALIDATE THE MODEL. /AUTHOR/

  • Supplemental Notes:
    • Tm-3078/102/00, 3522-032,CPR-11-4191
  • Corporate Authors:

    System Development Corporation

    2500 Colorado Avenue
    Santa Monica, CA  United States  90409

    Bureau of Public Roads /US

    400 7th Street, SW
    Washington, DC  United States  20590
  • Authors:
    • Gafarian, A
    • Hayes, E
  • Publication Date: 1969-6-30

Subject/Index Terms

Filing Info

  • Accession Number: 00203156
  • Record Type: Publication
  • Source Agency: Bureau of Public Roads /US
  • Files: TRIS
  • Created Date: Jul 14 1970 12:00AM