OVERTAKING AND PASSING REQUIREMENTS AS DETERMINED FROM A MOVING VEHICLE

BY PHOTOGRAPHIC METHODS OBSERVERS IN A MOVING CAR WERE ABLE TO MEASURE THE TIMES REQUIRED BY CARS OVERTAKING THEM TO PASS UNDER VARIOUS CONDITIONS. IT WAS FOUND THAT DRIVERS VARIED WIDELY IN THE SPEEDS, DISTANCES, AND TIMES WHICH THEY NEEDED TO OVERTAKE AND PASS ANOTHER VEHICLE. DISTANCE NEEDED INCREASED WITH SPEED. AT 30 MILES PER HOUR 650 FT. WERE REQUIRED AND AT 50 MILES PER HOUR 1,050 FT. WERE REQUIRED BY THE AVERAGE DRIVER (MEDIAN VALUES). IN ORDER TO TAKE IN 80 PERCENT OF THE DRIVERS APPROXIMATELY 1,200 FT. WOULD BE REQUIRED AT 50 MILES PER HOUR FOR AN ACCELERATIVE TYPE OF PASS. THE TOTAL TIME REQUIRED TO OVERTAKE AND PASS ALSO INCREASED SOMEWHAT AS SPEED INCREASED. THUS, AT 30 MILES PER HOUR THE AVERAGE DRIVER TOOK 8 1/2 SEC. AND AT 50 MILES PER HOUR 9 1/2 SEC. TO COMPLETE AN ACCELERATIVE TYPE OF PASS (MEDIAN VALUES). THE TIME VARIED FROM A MINIMUM OF 6 SEC. TO A MAXIMUM OF 20 SEC. IN INDIVIDUAL CASES AT SPEEDS FROM 30 TO 50 MILES PER HOUR. FROM THE SAFETY POINT OF VIEW IT IS OF INTEREST TO SEE WHAT CLEARANCES WERE ALLOWED BY THE PASSING DRIVERS BOTH TO THE REAR AND TO THE FRONT OF THE VEHICLE BEING PASSED. THE CLEARANCE TO THE REAR SHOWED A MEDIAN VALUE OF 45 FT. AT 50 MILES PER HOUR IN THE ACCELERATIVE TYPE OF PASS, AND THE CLEARANCE TO THE FRONT SHOWED A MEDIAN VALUE OF ABOUT 60 FT. HOWEVER, SOME DRIVERS APPROACHED AS CLOSE AS 10 FT. TO THE REAR AND CUT IN AS CLOSE AS 30 FT. IN FRONT OF THE OVERTAKEN VEHICLE AT 50 MILES PER HOUR. THE CLEARANCE DISTANCES WERE FOUND TO BE SHORTER IN THE NEW ENGLAND AREA, WHERE CROOKED AND HILLY ROADS ARE THE RULE, THAN THEY, WERE IN THE OPEN COUNTRY OF THE WEST AND MIDWEST, WHERE FAIRLY LONG CLEAR DISTANCES PREDOMINATE. THE DRIVERS IN THE FIRST AREA WERE APPARENTLY INDUCED TO PASS UNDER CONDITIONS WHICH WERE CONSIDERED HAZARDOUS BY THE DRIVERS IN THE AREAS WHERE LONGER CLEAR DISTANCES WERE FREQUENTLY AVAILABLE. THUS THE IMPORTANCE OF PROVIDING SUFFICIENT CLEAR SIGHT DISTANCE ON HIGHWAYS IS DEMONSTRATED. /AUTHOR/