COMPARATIVE FREEWAY STUDY

THIRTY-THREE SECTIONS /200 MILES/ OF FREEWAYS WITH WIDELY DIVERGENT ACCIDENT RATES WERE ANALYZED. THE FREEWAY SECTIONS WERE EITHER GEOGRAPHICALLY SEPARATE OR ESTABLISHED BY VIRTUE OF A CHANGE IN TRAFFIC VOLUME, ACCIDENT RATE, DESIGN CHARACTERISTICS OR YEAR BUILT. A TOTAL OF 11,384 ACCIDENTS WERE INCLUDED. THESE ACCIDENTS OCCURRED DURING THE COURSE OF 9,198 MILLION VEHICLE-MILES OF TRAVEL. THE AVERAGE ACCIDENT RATE FOR THE 33 SECTIONS IS 1.24 ACCIDENTS PER 1,000,000 VEH.-MI. THE ACCIDENT RATES FOR THE INDIVIDUAL SECTIONS RANGE FROM 4.52 TO 0.60 ACCIDENTS PER 1,000,000 VEH.-MI. THE PRIMARY PURPOSE OF THE FIRST PART OF THE STUDY WAS TO EXAMINE THOSE FREEWAY DESIGN CHARACTERISTICS RELATED TO ACCIDENT FREQUENCY. AMONG THESE WERE RAMP TERMINAL SHAPES, BRIDGE WIDTHS, TYPE OF INTERCHANGE, AND INTERCHANGE SPACING. ESPECIALLY SIGNIFICANT WAS THE TENTATIVE FINDING THAT ACCIDENT RATES RISE SHARPLY WITH AVERAGE LANE VOLUME. HUMAN FACTORS WERE CONSIDERED HOMOGENIOUS THROUGHOUT THE SECTIONS UNLESS THEY OBVIOUSLY PLAYED AN UNUSUAL ROLE IN A SECTIONS ACCIDENT HISTORY. PART TWO IS A DISCUSSION OF INDIVIDUAL SECTIONS AND AN ATTEMPT TO EXPLAIN THEIR PARTICULAR ACCIDENT HISTORY.