Cross section elements safety effects

Geometric design elements of rural two-lane highways that are related to crash frequencies include road, shoulder, and lane width. Increasing width is for the most part associated with decreasing crash numbers, especially at high volumes and, for shoulder width, in curves. However, at low volumes, increasing road and lane width may be associated with increasing crash numbers. At a given total road width, it is in most cases preferable (from a safety perspective) to have wide shoulders and narrow lanes. Increasing the number of lanes is mostly associated with decreasing crash numbers, mainly because it also is associated with other improvements. Increasing lane numbers may increase crash numbers when lanes are narrowed or the median omitted. Medians are generally associated with decreasing crash numbers. Passing lanes were also found to reduce crashes.