Geometric design inconsistencies on two-lane rural roads are often characterized through strong operating speed reductions between successive design elements and great disparities between the selected design speed and the measured operating speed, as well as deficiencies between side friction demanded and side friction assumed. Critical driving maneuvers, especially on older roads and unexpected sharp curves, are the results of those operational features; consequently, the safety level decreases. Accidents are the measurable evidence of design, construction and signing deficiencies. Eight curved sites with high accident frequencies were selected through an exactly defined procedure. Three different techniques were used to collect traffic operational data on the selected curves and these are described. The obtained analyzed data reveal main safety problems on all curves. It is proved that an appropriate judgement of the sharpness of the curve from an approach tangent is difficult for drivers and additionally complicated by variations in the length of curvature, vertical alignment and the roadside. To improve the safety on critical locations without changes in the horizontal and vertical alignment, a new traffic warning device is proposed that would give the driver more accurate and effective information about the curve ahead. As shown in this paper, design criteria for curves on two-lane rural roads are related to roadside features, which should simplify a driver's decision of the adequate driving and speed behavior according to the curve characteristics.
Samenvatting