Evaluation of Zero-Length Vertical Curves

To evaluate the use of zero-length vertical curves with respect to Texas Department of Transportation design practice, construction results, and vehicle dynamics, and to compare zero-length vertical curves with minimum-length design vertical curves, 20 zero-length vertical curves and 15 minimum-length vertical curves were evaluated. Evaluations performed included examinations of sight distance for zero-length vertical curves, surveying roadway profiles, and measuring vertical accelerations. Sight distance criteria were found to be generally inapplicable below 2 percent for sag vertical curves. For crest vertical curves, sight distance criteria were inapplicable below 1 percent for design speeds of 90 km/h or less and inapplicable below 0.5 percent for design speeds of 100 to 120 km/h. The results of vertical acceleration testing showed that, below 0.5 percent grade change, no practical difference was found between zero-length and minimum-design-length vertical curves. Between 1.0 and 0.5 percent grade change, significantly higher accelerations were measured for high-speed tests on zero-length vertical curves. Finally, it was found that zero-length vertical curves were more likely to meet drainage grade requirements than minimum-design-length vertical curves were.