DEVELOPING TRAFFIC INDICES FOR THE DETECTION OF HIGH ACCIDENT POTENTIAL HIGHWAYS IN NORTH CAROLINA
A SYSTEMATIC AND LARGE SCALE INVESTIGATION IS REPORTED OF THE CORRELATION OF MEAN NUMBER OF SPEED CHANGES WITH ACCIDENT RATES FOR SPECIFIC SECTIONS OF HIGHWAY. SEVERAL FACILITIES OF DIFFERING FUNCTIONAL CLASSIFICATIONS AND VEHICLE-MILE ACCIDENT RATES WERE SELECTED FOR TEST RUNS WITH THE RESEARCH VEHICLE. IT WAS CONCLUDED THAT THE MEAN NUMBER OF SPEED CHANGES PER MINUTE IS MATHEMATICALLY A FUNCTION OF ACCELERATION NOISE. HYPOTHESES INVOLVED IN THE INVESTIGATION ARE: (1) A UNIQUE SPEED CHANGE DISTRIBUTION FUNCTION EXISTS WITH ITS ASSOCIATED MEAN AND STANDARD DEVIATION FOR EACH AND EVERY DRIVER ON A GIVEN FACILITY WHEN DRIVING IN THE ABSENCE OF ALL OTHER TRAFFIC, (2) GIVEN A PARTICULAR SET OF TRAFFIC AND GEOMETRIC DESIGN CONDITIONS, A DRIVER WILL TRY TO MAINTAIN A UNIFORM VELOCITY OVER THE ROUTE, THOUGH NEVER QUITE SUCCEEDING, (3) GIVEN A FACILITY AND A GROUP OF DRIVERS, THE TRAFFIC STREAM WILL YIELD A SPEED CHANGE DISTRIBUTION UNIQUE FOR THAT FACILITY, (4) THE MEAN AND STANDARD DEVIATION OF THE SPEED CHANGE DISTRIBUTION FOR THE TRAFFIC STREAM WILL BE SIGNIFICANTLY DIFFERENT FOR THE VARIOUS FUNCTIONAL CLASSIFICATIONS, AND (5) THE MEAN AND STANDARD DEVIATION OF THE HIGHWAY FACILITY'S ACCELERATION DISTRIBUTION FUNCTION IS DIRECTLY RELATED TO THAT FACILITY'S TRUE ACCIDENT POTENTIAL AND TRUE ACCIDENT RATE. HIGHWAY SECTIONS SELECTED FOR INVESTIGATION VARIED FROM A 2-LANE RURAL SECONDARY ROAD TO A 4-LANE DIVIDED CONTROLLED ACCESS URBAN EXPRESSWAY. SPEED CHANGE DATA WERE MEASURED USING THE GREENSHIELD-PLATT DRIVOMETER WHICH WAS INSTALLED IN A TEST CAR. THIS PERMITTED MEASUREMENT ON A PER MINUTE BASIS OF THE NUMBER OF THE ABSOLUTE FOUR MPH SPEED CHANGES WHICH OCCURRED DURING A PARTICULAR RUN. THE MEAN AND STANDARD DEVIATION FOR EACH HIGHWAY TRIP WERE CALCULATED AND USED IN THE ANALYSIS. THE MEAN AND STANDARD DEVIATION WERE ANALYZED WITHIN EACH OF TEN LATIN SQUARES IN WHICH THE DATA WERE COLLECTED. THE DATA WERE THEN COMBINED AND AN ANALYSIS OF VARIANCE EXECUTED TO TEST THE TOTAL SIGNIFICANCE OF THE VARIOUS EFFECTS. RESEARCH RESULTS INDICATED: (1) THE MEAN NUMBER OF ABSOLUTE FOUR MPH SPEED CHANGES PER UNIT OF TIME IS A MATHEMATICAL FUNCTION OF ACCELERATION NOISE, (2) COMBINED ANALYSIS OF VARIANCE FINDINGS INDICATED THAT THE EFFECT OF THE HIGHWAY FACILITY ON THE MEAN NUMBER OF SPEED CHANGES IS HIGHLY SIGNIFICANT AND THE EFFECT OF HIGHWAY DIRECTION IS STATISTICALLY SIGNIFICANT, AND THE TIME OF DAY EFFECT IS SIGNIFICANT BUT NOT LARGE, (3) FROM AN INSPECTION OF THE DIFFERENCE OF MEAN VALUES FOR THE VARIOUS FACTS INVESTIGATED, THE ONLY EFFECT OF PRACTICAL IMPORTANCE IS THAT OF THE HIGHWAY FACILITY, (4) THE OVERALL MEAN NUMBER OF ABSOLUTE FOUR MPH SPEED CHANGES FOR THE VARIOUS FACILITIES ARE STATISTICALLY DIFFERENT FROM EACH OTHER WITH THE EXCEPTION OF TWO, AND (5) A VISUAL COMPARISON BETWEEN THE MEAN NUMBER OF ABSOLUTE FOUR MPH SPEED CHANGES AND ACCIDENT RATES FOR THE SIX FACILITIES INVESTIGATED REVEALED A RANK ORDER CORRELATION WITH THE EXCEPTION OF ONE FACILITY.
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Supplemental Notes:
- Proj No Erd-110-67-6, PART 1, PP 1-95, 10 FIG, 53 TAB, 16
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Corporate Authors:
North Carolina State Highway and Public Works Commission
P.O. Box 25201, 1 South Wilmington Street
Raleigh, NC United States 27611 - Publication Date: 1968-1
Subject/Index Terms
- TRT Terms: Acceleration (Mechanics); Analysis of variance; Crash rates; Drivers; Expressways; Four lane highways; Geometric design; Highways; Mathematical analysis; Mean (Statistics); Rural highways; Standard deviation; Testing; Traffic speed; Vehicle miles of travel
- Uncontrolled Terms: Change
- Old TRIS Terms: Drivometer; Mean (Statistical)
- Subject Areas: Data and Information Technology; Highways; Safety and Human Factors;
Filing Info
- Accession Number: 00219980
- Record Type: Publication
- Files: TRIS
- Created Date: Jun 18 1994 12:00AM