Operational Effects of Wide Edge Lines Applied to Horizontal Curves on Two-Land Rural Highways

摘要

The Pennsylvania Department of Transportation and other state transportation agencies are required to provide edge line delineation on two-lane arterials when traffic volumes exceed 6,000 vehicles per day and the pavement width is at least 20 feet. Other combinations of pavement width and traffic volume may also warrant edge line delineation. The standard edge line width is 4 inches; however, an edge line width of 8 inches can provide greater emphasis for motorists. There is a need to evaluate the effectiveness of providing wider edge lines on horizontal curves to determine if they provide improved delineation for motorists on two-lane highways. The objective of this project was to evaluate the operational effects of using wider edge lines on horizontal curves along two-lane rural highways. A before-after observational study with comparison sites was used to evaluate the change in several performance measures, including mean speed, speed variance, encroachment frequency, mean lateral vehicle position in the travel lane, lateral vehicle position variance, and speed and lateral vehicle position differential between the tangent and midpoint of a horizontal curve. Day and night time periods were considered as were approach tangent and horizontal curve locations. The effects of vehicles traveling in the opposing travel lane were also considered in the evaluation. The results indicate that wide edge lines, applied to horizontal curves on two-lane rural highways in Pennsylvania, do not consistently change the encroachment proportion along curves, nor do they consistently change driver behavior patterns at all treatment locations as measured by speed and lateral vehicle position. The location of speed deceleration, based on a subjective assessment of speed profile plots, provides evidence that drivers recognize curves at night from a greater distance with wide edge lines when compared to similar curves with standard, 4-inch-wide lines.