THE DISTRIBUTION AND TREND OF FREE SPEEDS ON TWO-WAY RURAL HIGHWAYS IN NEW SOUTH WALES

RESULTS ARE PRESENTED OF AN ANALYSIS OF 'FREE' SPEEDS MEASURED AT 31 LOCATIONS ON SECTIONS OF TWO-LANE TWO-WAY RURAL HIGHWAYS IN NEW SOUTH WALES DURING THE PERIOD BETWEEN 1963 AND 1967. FREE SPEEDS ARE MEASURES OF DRIVERS' DESIRED SPEEDS AND ARE THEREFORE MEASURED ONLY ON ISOLATED VEHICLES OR ON THOSE LEADING A PLATOON. THE LOCATIONS SELECTED WERE ON STRAIGHT LENGTHS OF ROAD HAVING BITUMEN OR CONCRETE SURFACES, WITH GRADIENTS RANGING FROM 0 TO 10 PER CENT, AND WITH A PRIME FACIE SPEED LIMIT OF 50 M.P.H. THE IMPORTANT FINDINGS ARE AS FOLLOWS: (1) THE SPEED DISTRIBUTIONS OF CARS MEASURED AT PRACTICALLY ALL THE SITES CAN BE REPRESENTED BY A 'STANDARDIZED' NORMAL DISTRIBUTION WITH A STANDARD DEVIATION OF 0.17 TIMES THE MEAN. (2) THE FREE SPEEDS OF CARS WERE INVARIABLY HIGHER THAN THE SPEEDS OF TRUCKS EVEN WHEN TRAVELLING ON DOWNGRADE. (3) AT ANY GIVEN SITE THE MEAN SPEED OF VEHICLES TRAVELLING ON DOWNGRADE WAS ALWAYS HIGHER THAN THAT ON UPGRADE. (4) GRADIENTS, SHOULDER AND PAVEMENT WIDTHS, AND SIGHT DISTANCE AFFECTED FREE SPEEDS. IN GENERAL, AN INCREASE IN GRADIENTS EITHER UPGRADE OR DOWNGRADE DECREASED SPEED; INCREASE IN PAVEMENT WIDTH, SHOULDER WIDTH AND SIGHT DISTANCE, ON THE OTHER HAND, INCREASED THE FREE SPEED. /AUTHOR/

• Supplemental Notes:
  • Vol 4, Pt 1, PP 791-814
• Corporate Authors:

  ARRB

  Melbourne, Victoria  Australia 
• Authors:
  • Leong, H J
• Conference:
  • Australian Road Research Board Conference Proc
• Publication Date: 0

Media Info

• Serial:
  • Issue Number: 0

Subject/Index Terms

• TRT Terms: Highway grades; Normal distributions; Pavements; Road shoulders; Rural highways; Sight distance; Slopes; Speed; Studies; Traffic speed; Two lane highways; Width
• Uncontrolled Terms: Free speed
• Old TRIS Terms: Pavement width; Speed studies
• Subject Areas: Highways; Operations and Traffic Management; Pavements;

Filing Info

• Accession Number: 00227263
• Record Type: Publication
• Source Agency: Traffic Systems Reviews & Abstracts
• Files: TRIS
• Created Date: Jul 27 1970 12:00AM