AN EVALUATION OF THE GRAVITY MODEL TRIP DISTRIBUTION

THE GRAVITY MODEL TRIP DISTRIBUTION WAS CALIBRATED AND TESTED USING A SMALL SIZED URBAN AREA, WACO, TEXAS. THE STUDY OBJECTIVES WERE TO: (1) DETERMINE THE APPROPRIATE TRIP PURPOSE STRATIFICATION TO BE USED WITH A GRAVITY MODEL TRIP DISTRIBUTION FOR WACO, TEXAS AND OTHER URBAN AREAS OF SIMILAR CHARACTER, AND (2) EVALUATE THE ABILITY OF THE GRAVITY MODEL TO REPRESENT THE ACTUAL TRIP BEHAVIOR AS ESTIMATED FROM A DWELLING-UNIT SURVEY. A TWO-PURPOSE MODEL COMPOSED OF HOME-BASED AND NONHOME-BASED TRIPS, RESPECTIVELY, APPEARED TO BE OPTIMAL FOR THE WACO AREA. SUBSTANTIAL RIVER CROSSING BIAS WAS OBSERVED AND CORRECTED WITH A RIVER TIME BARRIER. THE STUDY PRESENTED NO VISABLE EVIDENCE TO SUPPORT ANY ADJUSTMENTS FOR BIAS ATTRIBUTED TO SOCIAL-ECONOMIC CHARACTERISTICS. INTRAZONAL TRIPS WERE RECOGNIZED TO BE AMONG THE HIGHEST VOLUME MOVEMENTS, AND WERE OBSERVED TO EXHIBIT SIGNIFICANT DISCREPANCIES BETWEEN GRAVITY MODEL AND SURVEY DATA VOLUMES. THE GRAVITY MODEL WAS OBSERVED TO ALLOCATE SOME TRIPS TO NEARLY EVERY CONCEIVALBE ZONE PAIR COMBINATION. CONVERSELY, ABOUT 80 PERCENT OF THE SURVEY DATA TRIP MATRIX WAS FOUND TO BE VACANT OF TRIPS. INTO THESE VACANT SURVEY DATA CELLS, THE GRAVITY MODEL LOCATED ABOUT ONE-THIRD OF THE TOTAL TRIPS. THE GRAVITY MODEL SORTED THE MOVEMENTS OBSERVED IN THE SURVEY DATA BY THIS MANY TRIPS. ON AN INDIVIDUAL ZONE-TO-ZONE BASIS, A VIRTUALLY HAPHAZARD TENDENCY WAS OBSERVED WITH REGARD TO OVER OR UNDER ESTIMATION. ONLY ABOUT 80 PERCENT OF ALL ZONE PAIRS WERE FOUND TO HAVE A GRAVITY MODEL VOLUME WITHIN FIVE TRIPS OF THE SURVEY DATA VOLUME. DEVIATIONS AS LARGE AS SEVENTEEN TRIPS HAD TO BE TOLERATED BEFORE 95 PERCENT OF THE ZONE PAIRS FELL WITHIN THE TOLERANCE RANGE.

• Supplemental Notes:
  • Rr60-13, 96 PP, 39 FIG, 9 TAB, 3 REF, 2 APP
• Corporate Authors:

  Texas Transportation Institute

  Texas A&M University System, 1600 E Lamar Boulevard
  Arlington, TX  United States  76011
• Authors:
  • Long, G D
• Publication Date: 1968-8

Subject/Index Terms

• TRT Terms: Gravity models; Traffic assignment; Traffic surveys; Traffic volume; Trip generation
• Uncontrolled Terms: Intrazonal trips
• Subject Areas: Highways; Operations and Traffic Management;

Filing Info

• Accession Number: 00225603
• Record Type: Publication
• Files: TRIS
• Created Date: Mar 16 1970 12:00AM