EFFECT OF ROADWAY WIDTH ON TRAFFIC OPERATIONS-TWO-LANE CONCRETE ROADS

EXTENSIVE SPEED-PLACEMENT STUDIES WERE CONDUCTED IMMEDIATELY PRIOR TO WORLD WAR II. CONCLUSIONS INCLUDE THE FOLLOWING. SHOULDERS WIDER THAN 4 FT DO NOT EFFECT PAVEMENT WIDTH FOR MOVING TRAFFIC. GRASS AND GRAVEL SHOULDERS HAVE THE SAME EFFECT ON TRANSVERSE POSITIONS OF MOVING VEHICLES. WITH 18 AND 20 FT PAVEMENTS, BITUMINOUS SHOULDERS INCREASE THE EFFECTIVE WIDTH ABOUT 2 FT. LIP CURBS ON 20 FT SURFACES REDUCES EFFECTIVE WIDTH ABOUT 1 FT IN THE DAYTIME. PAVEMENTS LESS THAN 22 FT WIDE ARE HAZARDOUS EVEN FOR MODERATE VOLUMES OF MIXED TRAFFIC; DRIVERS DO NOT REDUCE SPEEDS WHEN MEETING ON NARROW PAVEMENTS. A 24 FT PAVEMENT IS REQUIRED TO PROVIDE DESIRED CLEARANCES FOR COMMERCIAL TRAFFIC. /AUTHOR/