MARKING HIGHWAY CURVES WITH SAFE SPEED INDICATIONS

THE MAJORITY OF STATES CONTACTED IN A QUESTIONNAIRE REPORTED THAT A BALL-BANK INDICATOR READING OF 10 DEG. WAS THE MOST SATISFACTORY INDICATION OF SAFE SPEED. CHARTS AND GRAPHS OF DRIVING TESTS ON CURVES CONDUCTED BY THE RESEARCH STAFF OF THE IOWA ENGINEERING EXPERIMENT STATION, THE GENERAL MOTORS PROVING GROUND, AND BY ENGINEERS IN SEVERAL STATES, PROVIDE FACTUAL DATA ON PRACTICALLY EVERY PHASE OF CAR OPERATION ON CURVES RELATED TO SAFE SPEEDS, SUCH AS VARIATIONS IN BALL-BANK READINGS FOR VARIOUS MAKES OF CARS AT VARIOUS SPEEDS, THE BODY ROLL ANGLES OF CARS, THE SIDEWAYS FRICTIONAL FACTOR, STEERING ANGLES AND STEERING FORCES, THE EFFECT OF SURFACE ROUGHNESS AND ROAD SLIPPERINESS, AND THE VISIBILITY ON CURVES AT NIGHT WITH SEALED BEAMS OR COMMON TYPE HEADLIGHTS. IN GENERAL IT WAS FOUND THAT A BALL-BANK ANGLE OF 10 DEG. PROVIDED AN AMPLE MARGIN OF SAFETY FOR ALL OF THE ABOVE FACTORS EXCEPT EXTREME CONDITIONS OF SURFACE SLIPPERINESS, OR FOR SNOW AND ICE CONDITIONS. THE PRACTICE IN REGARD TO THE SIZE, SHAPE, AND COLOR OF SIGNS WAS FOUND TO VARY ALTHOUGH A SIGN APPROXIMATELY ONE FOOT SQUARE WITH BLACK NUMERALS AND LETTERS ON A WHITE BACKGROUND WAS GENERALLY USED. THE STATE OF ILLINOIS USES WHITE NUMERALS AND LETTERS ON A BLACK BACKGROUND. THE BEFORE AND AFTER STUDIES REPORTED BY SEVERAL STATES INDICATED THAT SPEEDS WERE MORE NEARLY UNIFORM ON MARKED CURVES THAN ON UNMARKED CURVES AND THAT THERE WAS LESS CONGESTION OF TRAFFIC ON THESE CURVES. THE ACCIDENT EXPERIENCE ON A 95-MILE SECTION IN INDIANA WAS PARTICULARLY NOTEWORTHY. IN 1939 AND 1940 THERE WERE 10 FEWER FATALITIES, 12 FEWER PERSONS INJURED, 36 FEWER ACCIDENTS ON CURVES, AND APPROXIMATELY $9,000,000 LESS PROPERTY DAMAGE DURING THE TWELVE MONTH PERIOD IN WHICH THE SIGNS WERE IN OPERATION THAN IN THE PREVIOUS 12 MONTHS PERIOD. THE GREATEST ADVANTAGE TO THE MOTORIST PROVIDED BY SPEED SIGNS IS THAT THEY ELIMINATE THE SURPRISE ELEMENT WHEN COMING INTO A LOW SPEED CURVE, ESPECIALLY AN ISOLATED CURVE, WHERE THE APPROACH SPEED MAY BE 50 TO 60 MPH AND THE SAFE SPEED ON THE CURVE 30 TO 35 MPH. /AUTHOR/

• Record URL:
  https://onlinepubs.trb.org/Onlinepubs/hrbproceedings/20/20-024.pdf
• Supplemental Notes:
  • Vol 20, pp 399 - 428, 15 FIG, 5 TAB. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved.
• Authors:
  • Moyer, R A
  • Berry, D S
• Publication Date: 1941

Media Info

• Media Type: Digital/other
• Monograph Title: Proceedings of the Twentieth Annual Meeting of the Highway Research Board Held at Washington, D.C. December 3-6, 1940
• Serial:
  • Highway Research Board Proceedings
  • Volume: 20
  • Publisher: Highway Research Board

Subject/Index Terms

• TRT Terms: Crash rates; Driver information systems; Drivers; Highway curves; Information management; Information, data, and knowledge; Safety factors; Speed; Traffic crashes; Traffic signs
• Subject Areas: Data and Information Technology; Highways; Operations and Traffic Management; Safety and Human Factors;

Filing Info

• Accession Number: 00225971
• Record Type: Publication
• Files: TRIS, TRB
• Created Date: Aug 15 1971 12:00AM