Poor Visibility: A Common Cause of Wrong-way Driving

About the report:

On-site investigations were made of interchanges in Virginia, some of which had been the site of wrong-way entries and some of which had not, and of intersections that had experienced wrong-way incidents. From the observations made on-site it has been concluded that poor visibility at intersections due to road geometrics and incomplete or improper guidance signs and pavement markings is a major cause of wrongway entries at day and night. This report discusses the causes of poor visibility and presents seven case studies of interchanges and intersections. Several recommendations for preventing wrong-way entries for a given set of conditions are given below. The locations of road signs and pavement markings should be designed on the basis of night visibility rather than day visibility. The application of the theory of a "cone of vision" for placement of signs needs to be modified. The "keg of legibility" as developed in this investigation for night legibility of signs seems to be more applicable. At intersections with poor geometrics, such as differences in elevation between the opposite lanes of 4-lane divided highways, the crossroads sloping downward from divided highways, or wide crossovers, could lead to wrong-way entries. A divided highway intersection diagrammatic sign placed at the junction of the crossroad and the divided highway will inform the driver of the geometry of the intersection during day and night. Also in some places a left turn diagrammatic sign placed at the nose of the median will inform the driver of the location of the nose of the left median and the need for turning around it. There is a great need for pavement markings that will channelize vehicle movements at night. To discourage a driver from entering an exit ramp at night when his depth of vision is low, the pavement edge marking should be continued across the exit ramp or the stop line should be brought closer to the edge of the crossroad such that it is visible to the driver on the crossroad.

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