SPEED HABITS OBSERVED ON A RURAL HIGHWAY

FIELD DATA COMBINED FOR 2 YEARS AND POSTCARD-SURVEY INFORMATION FURNISHED A BASIS OF ANALYSIS OF THE RELATION IN THIS STUDY OF AVERAGE SPEED TO VARIOUS DRIVER AND CAR CHARACTERISTICS. HIGHER SPEEDS WERE ASSOCIATED WITH YOUNGER DRIVERS, LARGER AMOUNTS OF TRAVEL, AND NEWER CARS. BUT NO COMBINATION OF THESE FACTORS COULD EXPLAIN MORE THAN A SMALL FRACTION OF THE TOTAL VARIANCE IN SPEED. THE REAPPEARANCE OF DRIVERS AND INDIVIDUAL SPEEDS AND AVERAGE SPEEDS FOR ALL OBSERVATIONS WERE ANALYZED TO ESTABLISH FEATURES OF THE ACTUAL SPEED DISTRIBUTIONS PRELIMINARY TO THE STATISTICAL DEVELOPMENT OF THE ANALYSIS OF SPEED VARIANCE BETWEEN GROUPS OF DRIVERS HAVING DIFFERENT AVERAGE SPEEDS AND AMONG INDIV- IDUAL DRIVERS. TO COMPUTE THE PERCENTAGE OF SPEEDS ABOVE A SPECIFIED VALUE WHICH ARE DRIVEN BY ANY GIVEN PERCENTAGE OF THE FASTEST DRIVERS, A MODEL WAS DEVELOPED FOR A THEORETICAL SPEED DISTRIBUTION BASED ON ASSUMPTIONS OF THE DRIVER'S SPEED BEHAVIOR AND THE EMPIRICAL VALUES OF AVERAGE SPEED AND 'WITHIN' AND 'BETWEEN' SPEED VARIANCES. PROCEDURES WERE DEVELOPED FOR TESTING AND THEORETICAL DEDUCTIONS AGAINST THE OBSERVED DATA. THE AGREEMENT BETWEEN THEORY AND OBSERVATION IS EXCELLENT. IT WAS SHOWN, FOR EXAMPLE, THAT ABOUT A THIRD OF ALL DRIVERS HAVE 85- PERCENTILE VALUE IN THE SPOT- SPEED DISTRIBUTION, AND IF A SET OF DRIVERS ARE ALL OBSERVED AS MANY AS SEVEN TIMES, MORE THAN HALF OF THEM CAN BE EXPECTED TO EXCEED THE 85-PERCENTILE SPEED AT LEAST ONCE. CURVES WERE DEVELOPED SHOWING THE PERCENTAGES OF SPEEDS ABOVE SPECIFIED VALUES WHICH ARE DRIVEN BY VARIOUS PERCENTAGES OF THE FASTEST AND SLOWEST DRIVERS. THE FASTEST 10 PERCENT OF THE DRIVERS PROVIDE A THIRD OF ALL THE SPEEDS FASTER THAN THE 85-PERCENTILE. AN AVERAGE DRIVER, I.E., A DRIVER WHOSE AVERAGE SPEED IS EQUAL TO THE OVERALL AVERAGE, CAN BE EXPECTED TO EXCEED THE 85-PERCENTILE SPEED ABOUT 11 PERCENT OF THE TIME. THE FASTEST 15 PERCENT OF THE DRIVERS CONTRIBUTE 46 PERCENT OF ALL THE SPEEDS OVER THE 85 PERCENTILE SPEED. /AUTHOR/