OFFTRACKING CHARACTERISTICS OF TRUCKS AND TRUCK COMBINATIONS

MAXIMUM SIZES AND WEIGHTS OF COMMERCIAL MOTOR VEHICLES (EXCEPT LENGTH AND HEIGHT) WERE EFFECTIVELY FROZEN BY THE FEDERAL-AID-ACT OF 1956 WHICH PROVIDED FOR FINANCING AND CONSTRUCTION OF THE NATIONAL SYSTEM OF INTERSTATE AND DEFENSE HIGHWAYS. THE ACT ALSO PROVIDED FOR STUDIES TO DETERMINE THE MAXIMUM DESIRABLE DIMENSION AND WEIGHTS OF VEHICLES OPERATED ON THE FEDERAL-AID HIGHWAY SYSTEMS. THE FEDERAL SIZE AND WEIGHT REPORT EMPHASIZED THAT HEAVIER AND LARGER VEHICLES, IF ALLOWED TO OPERATE ON PUBLIC HIGHWAYS, MUST HAVE SAFETY AND PERFORMANCE CHARACTERISTICS EQUAL TO OR BETTER THAN EXISTING VEHICLES. THIS STUDY IS CONCERNED WITH THE ADEQUACY OF THE PHYSICAL HIGHWAY PLAN TO ACCOMODATE SUCH VEHICLES. THIS ANALYSIS DEALS WITH MEASUREMENT OR ESTIMATES OF OFFTRACKING ACCORDING TO THE GRAPHICAL AND MATHEMATICAL METHODS, AND BY MEANS OF VEHICLE MODELS. THE AMOUNT OF OFFTRACKING ASSIGNABLE TO, OR THE WIDTH OF TURNING TRACK REQUIRED BY VEHICLES OF KNOWN WHEEL BASE, OR COMBINATIONS OF UNITS OF KNOWN WHEEL BASE, EXECUTING TURNS OF GIVEN RADIUS AND LENGTH, IS A MATTER THAT IS NOT LIMITED IN INTEREST TO ITS RELATIONSHIP TO HIGHWAY DESIGN GEOMETRICS. THESE SERIES OF TESTS, WITH THE AID OF AN ADJUSTABLE VEHICLE MODEL, MAKE POSSIBLE THE FOLLOWING GENERAL CONCLUSIONS: (1) THERE ARE NO SIGNIFICANT DIFFERENCES IN THE RESULTS OF MAXIMUM OFFTRACKING MEASUREMENTS FOR THE SAME VEHICLE OR COMBINATION, WHETHER THEY BE DETERMINED BY MATHEMATICAL SOLUTION, BY THE GRAPHICAL METHOD, OR BY MEANS OF A VEHICLE MODEL, (2) FOUR VEHICLES WITH ASSUMED DIMENSIONS WERE SUBJECTED TO STUDY IN THE SEVERAL TURNING SITUATIONS WERE MADE A PART OF THIS ANALYSIS FOR THE PURPOSE OF COMPARING THREE METHODS FOR ARRIVING AT OFFTRACKING DISTANCES, UNDER STIPULATED ASSUMPTIONS OF CURVE RADIUS AND LENGTH; A MORE COMPREHENSIVE AND REPRESENTATIVE LIST OF FREQUENTLY ENCOUNTERED TYPES, LENGTHS, AND WHEEL BASES WITH MAXIMUM OFFTRACKING DISTANCES TO BE EXPECTED IN NEGOTIATION OF A 165 FOOT RADIUS CURVE IS GIVEN IN A TABLE AND ITS ACCOMPANYING CHART, (3) THE AMOUNT OF OFFTRACKING IS PRINCIPALLY RELATED TO THE LENGTHS OF WHEEL BASES OF THE VEHICLE'S COMPONENTS; THE SPACING OF THE AXLES AND POINTS OF ARTICULATION, (4) FOR A GIVEN RADIUS OF CURVATURE THE AMOUNT OF MAXIMUM OFFTRACKING OF ANY VEHICLE (COMBINATION) IS A FUNCTION OF THE SUM OF THE SQUARES OF THE COMPONENT WHEEL BASES, (5) THE PROPOSITION WAS CONFIRMED THAT THE AMOUNT OF OFFTRACKING DEPENDED UPON WHEEL BASES (AND HITCH DISTANCES), ANGLE OF TURN, AND RADIUS OF CURVATURE, AND (6) OFFTRACKING IS AFFECTED BY THE WAY IN WHICH THE VEHICLE IS DRIVEN INTO AND THROUGH THE TURN, BUT THE RECENT EXPERIMENT WITH ACTUAL VEHICLES HAVING INTERIOR MEASUREMENTS CLOSELY APPROXIMATELY THOSE OF THIS STUDY'S TYPICAL VEHICLES WAS IN AGREEMENT WITH THE OFFTRACKING REGISTERED BY THE MODEL.

  • Supplemental Notes:
    • Rept No 3, 48 PP, 17 FIG, 7 TAB, 6 REF
  • Corporate Authors:

    Western Highway Institute

    San Francisco, CA  United States 
  • Publication Date: 1970-2

Subject/Index Terms

Filing Info

  • Accession Number: 00203479
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Aug 26 1970 12:00AM