THE SAFETY ADVANTAGES OF BIGGER TRUCK

THE NATIONAL SAFETY COUNCIL STATES THAT THE TOTAL ACCIDENT RATE FOR ALL MOTOR VEHICLES COMBINED IS 14 PER 1 MILLION VEHICLE MILES. TRUCKS AS A GROUP HAVE AN ACCIDENT RATE OF 12.37 PER 1 MILLION VEHICLE MILES. WHEN JUST THE INTERCITY COMMON CARRIERS ARE CONSIDERED, THE ACCIDENT INVOLVEMENT RATE IS ONLY 3.58 ACCIDENTS PER MILLION VEHICLE MILES OF TRAVEL. THE ACCIDENT FREQUENCY RATIO FOR INTERSTATE TRUCKS OPERATED BY LARGE MOTOR CARRIERS (PRINCIPALLY BIG TRUCKS AND TRUCK AND TRUCK CONBINATIONS) IS ONLY 2.5. THE LONG MULTIPLE TRUCK COMBINATION IS CHOSEN BY TRUCK OPPONENTS AS THE MOST DANGEROUS HIGHWAY VEHICLE, CONTRARY TO VALID SAFETY STATISTICS. THE MOST WIDELY USED TRIPLES COMBINATION IS APPROXIMATELY 95 FEET LONG WHEN POWERED BY A 4X2 OR 4X4 TRUCK-TRACTOR AND APPROXIMATELY 98 FEET LONG WHEN A TADEM AXLE TRUCK-TRACTOR IS EMPLOYED. IT IS 96 INCHES WIDE, ALTHOUGH TEST OPERATIONS IN ALBERTA WERE HIGHLY SUCCESSFUL USING 102-INCH WIDE TRAILERS. A MOST IMPORTANT SAFETY FACTOR IN ANY HIGHWAY VEHICLE IS BRAKING, NOT ONLY BRAKING DISTANCE, BUT ALSO THE STABILITY DURING THE BRAKING MANEUVER. IN THE AREAS OF BREAKING AND STABILITY, THE TRIPLES COMBINATION HAS SOME INHERENT NATURAL ADVANTAGES OVER LIGHTER AND SHORTER VEHICLES. THE TRIPLES COMBINATION WITH ITS 7 OR 8 BRAKED AXLES, LARGE BRAKED DRUMS AND 26 TO 30 TIRES HAS CONSIDERABLE AREA OVER WHICH TO DISSIPATE THE ENERGY OF MOTION IN THE FORM OF HEAT. IN FACT, DUE TO THE LOWER AVERAGE AXLE LOADS GENERALLY PREVAILING FROM BRIDGE FORMULA AXLE LOAD LIMITATIONS, TRIPLES HAVE A LOT OF SURPLUS BRAKING HORSEPOWER. SO TRIPLES COMBINATIONS, DUE TO REQUIRED AND ACCEPTED LOADING PRACTICE, ARE PROGRESSIVELY LIGHTER FROM FRONT TO REAR HEAVIEST AXLE BEING THE DRIVE AXLE AND THE SEMITRAILER BEHIND THE TRUCK-TRACTOR BEING THE HEAVIEST UNIT. THIS MEANS THAT THE REARMOST AXLE WILL HAVE THE MOST BRAKING EFFECTIVENESS, THE SECOND FROM THE REAR, THE NEXT BEST BRAKING EFFECTIVENESS, ETC. ON WET AND SLIPPERY PAVEMENTS, LARGE TRUCKS WITH THEIR HIGH PRESSURE TIRES NEVER HYDROPLANE AT NORMAL TRAFFIC SPEEDS. THE HIGHER AVERAGE COEFFICIENT OF FRICTION EXISTING DURING A WET STOP IS ANOTHER ADVANTAGE ENJOYED BY THE TRIPPLES COMBINATION. ANOTHER PERFORMANCE CHARACTERISTIC OF A TRIPLES COMBINATION WHICH CONTRIBUTES A HIGH FACTOR OF SAFETY IS ITS DYNAMIC OR OPERATIONAL STABILITY. TRIPLES COMBINATIONS CAN MANEUVER AND OFFTRACK AS WELL AS SOME CONVENTIONAL TRACTOR-SEMITRAILER COMBINATIONS SUCCESSFULLY USING STREETS AND HIGHWAYS. BIGGER TRUCKS, WHEN PROPERLY OPERATED UNDER REGULATED CONDITIONS, CAN HELP IMPROVE HIGHWAY SAFETY AS WELL AS MANY PROBLEMS OF CONGESTION, SMOKE AND NOISE.

• Supplemental Notes:
  • 18 Pp, 14 REF
• Corporate Authors:

  Western Highway Institute

  San Francisco, CA  United States 
• Authors:
  • Sherard, T D
• Publication Date: 0

Subject/Index Terms

• TRT Terms: Axles; Braking; Crash rates; Interstate transportation; Length; Motor vehicles; Safety; Stability (Mechanics); Tandem axle loads; Tractor trailer combinations; Trucks; Turning radius
• Old TRIS Terms: Tandem axles; Triple combination; Turning path
• Subject Areas: Highways; Motor Carriers; Safety and Human Factors;

Filing Info

• Accession Number: 00221075
• Record Type: Publication
• Files: TRIS
• Created Date: Oct 19 1970 12:00AM