The F+I accident rate for spiral curves was significantly higher than for standard curves for the total of all curve radii. The F+I accident rate for spiral curves was higher for curves with radii above 550 ft and about the same for curves with radii of 550 ft or less. The occurrence of F+I accidents on large radius curves (R > 1,150 ft) were few. The percent differences in the F+I accident rates between the standard curves and the spiral curves for this study appear to increase as the radii increases, although this is not certain due to the small accident sample for large radius curves.
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