Elements of Median Design in Relation to Accident Occurrence

THE PURPOSE OF THIS STUDY WAS TO COMPARE THE ACCIDENT HISTORIES OF DIFFERENT MEDIAN TYPES AND TO PROVIDE VERIFICATION OF GENERALLY RECOMMENDED MEDIAN WIDTHS AND SLOPES. A MAJOR LIMITATION OF THE ANALYSES WAS THE SMALL NUMBER OF POSSIBLE COMBINATIONS OF MEDIAN WIDTH AND CROSS SLOPE AVAILABLE FOR STUDY. THE ANALYSES REPORTED PROVIDED EVIDENCE FROM ACCIDENT HISTORIES TO SUPPORT THE GENERAL ASSUMPTION THAT WIDER MEDIANS ARE SAFER MEDIANS. IT WAS INDICATED THAT MEDIANS SHOULD BE A MINIMUM OF 30 TO 40 FT WIDE FOR HIGH-SPEED FACILITIES AND THAT FLAT SLOPES SHOULD BE PROVIDED; 4:1 SLOPES ARE INADEQUATE FOR MEDIANS LESS THAN 60 FT WIDE. THERE WAS AN INDICATION THAT 6:1 OR FLATTER SLOPES SHOULD BE USED. RAISED MEDIANS PROVIDED AN UNSUITABLE VEHICLE RECOVERY AREA ON RURAL HIGHWAYS AND WERE ALSO UNDESIRABLE FROM THE STANDPOINT OF ROADWAY SURFACE DRAINAGE. THE IRREGULAR INTERSTATE HIGHWAY MEDIANS THAT RESULT FROM INDEPENDENT ROADWAY ALIGNMENT SHOULD BE USED ONLY WITH ADEQUATE CLEAR ZONES IN THE MEDIAN. SHOULDERS 12 FT WIDE SHOULD BE PROVIDED WHERE GUARDRAIL IS TO BE USED.