TRAFFIC BEHAVIOR AND ON-RAMP DESIGN

THREE RAMP TERMINAL DESIGNS WERE PAINTED SUCCESSIVELY AT ONE ON-RAMP LOCATION. THE FIRST SEQUENCE OF OBSERVATIONS WAS MADE WITH THE RAMP CURB ENCROACHING ON THE SHOULDER (2 FT FROM EDGE OF FREEWAY PAVEMENT) AND A SECOND SEQUENCE WAS OBSERVED WITH THE RAMP CURB OFFSET SHOULDER WIDTH FROM THE FREEWAY PAVEMENT (IN THIS CASE 8 FT), RESULTING IN SIX SEPARATE STUDIES. SPEED AND PLACEMENT OF VEHICLES WERE RECORDED AND MOVIES WERE TAKEN DURING EACH PHASE. FREEWAY VOLUME VARIED FROM 2,400 TO 6,000 VPH, WHILE RAMP VOLUME VARIED FROM 240 TO 1,200 VPH. FINDINGS INCLUDE THE FOLLOWING: (1) ALL THREE DESIGNS RESULTED IN SIMILAR VEHICLE PATHS, BECAUSE ESSENTIALLY THEY WERE ALL LIBERAL DESIGNS AND TRAFFIC WAS ABLE TO DRIVE A NATURAL PATH. WHEN THE NOSE WAS OFFSET, A LONG GRADUAL TAPER (50:1) APPEARED TO CAUSE VEHICLES TO USE A GREATER PORTION OF THE RAMP THAN A PARALLEL RAMP OF THE SAME LENGTH, (2) SOMEWHAT MORE LENGTH WAS USED AT LOW VOLUMES THAN AT HIGH VOLUMES, EXCEPT DURING THE 8-FT OFFSET 50:1 TAPER PHASE, WHERE THE LENGTH USED WAS APPROXIMATELY CONSTANT FOR ALL VOLUMES, (3) MERGING DISTANCE REQUIRED AT HIGH TURNING SPEED IS AS GREAT AS THAT REQUIRED AT LOW SPEED, AND (4) THE NATURAL PATH OF NEARLY ALL VEHICLES IS CONTAINED WITHIN A 50:1 TAPER, AND THIS DESIGN PROVIDES SUFFICIENT ACCELERATION DISTANCE FOR ALL TURNING SPEEDS. IT IS CONCLUDED THAT RAMP TERMINAL DESIGN SHOULD BE STANDARDIZED AND A TENTATIVE STANDARD IS OFFERED TOGETHER WITH SUPPORTING DATA AND REASONING. /AUTHOR/

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  • Accession Number: 00225356
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Aug 19 1994 12:00AM