The following six types of median traffic dividers were constructed on the long island parkway system for experimental analysis: (1) narrow concrete wall with pipe, (2) narrow concrete wall, (3) concrete parabolic wall, (4) nine foot grass median with low 4 inch curb, (5) paint line divider (no physical separator), and (6) wide grass mall. In addition to the six types of median dividers, the test sites on limited access parkways provided the following features, different lane widths, different curb heights, tangent and curved roadway alignment, wide variation in traffic volumes, flat grades, elimination of the effects of all types of commercial vehicles and marginal interference. Speed tests and vehicle placement tests were conducted. Information from these traffic tests indicated the following tendencies: (1) drivers ride closer to the edge of the concrete parabolic wall-type divider than to any of the other types of medians tested, (2) the 6-inch paint line divider and the narrow wall-type divider have about the same effect on the positioning of cars in the centre lane, (3) main lines between two parallel streams of traffic cause motorists in the outside lane to drive closer to the centre median than when no lane lines are provided, (4) medians do not eliminate the common tendency of drivers to cut across horizontal curves, (5) clearance distance between cars and parallel streams of traffic grow wider as the roadway width increases and as the volume increases, (6) on relatively sharp curves the clearance distance between cars in parallel streams of traffic becomes less than on tangent sections, and (7) the distance from the edge of the pavement to cars in the outside lane is the same or about the same for equal pavement width, regardless of the type of centre median. (A)
Samenvatting