Speed Changes in the Vicinity of Horizontal Curves on Two-Lane Rural Roads

In some situations, the horizontal alignment of a road, particularly circular curves, are designed for reduced speeds compared to their adjacent sections to reduce costs and to avoid compromising the qualities of historical districts and areas of special value. Thus far, there is no sufficient research on driver behavior in the vicinity of curves with reduced standards. Speed transition behavior should be considered in designing spirals or tangent-to-curve sections where there is a difference in the design speed between the curve and the adjacent tangents. Driver behavior before and after horizontal curves was investigated and speed models for transition sections were developed. These models could be used to design transition sections and to assess the design consistency of two-lane rural roads. The results indicated that 66% of the speed reduction and 72% of the speed increase occurs on the tangents preceding and following the curves, respectively. In addition, the mean deceleration rate and the mean acceleration rate are 0.033 and $0.022(\mathrm{ft}∕\mathrm{s})∕\mathrm{ft}$ , respectively; or approximately 0.732 and $0.488\mathrm{m}∕{\mathrm{s}}^2$ , respectively, for a $16.1\mathrm{km}∕\mathrm{h}$ $(10\mathrm{mi}∕\mathrm{h})$ reduction.