EVALUATION OF ZERO-LENGTH VERTICAL CURVES

The objectives of the research were to evaluate the use of zero-length vertical curves with respect to Texas Department of Transportation (TxDOT) design practice, construction results, vehicle dynamics, and accident history, and to compare zero-length vertical curves to minimum design vertical curves (as specified by TxDOT). Researchers determined use of zero-length vertical curves using a questionnaire distributed to TxDOT personnel in all 25 districts. Seventy-one percent of the respondents had used zero-length vertical curves. In this study, 20 zero-length vertical curves and 15 minimum-length vertical curves were evaluated. Constraints limited grade change for the vertical curves to a maximum of 2%. Evaluation included surveying the roadway profile, measuring vertical acceleration, and investigating accident information. The results showed that: sight distance is not applicable to sag curves with grade changes below 2% and is applicable to crest curves with grade changes above 0.5% and design speeds over 100 km/h; below 0.5% grade change, comfort criteria for zero-length and minimum design vertical curves did not exhibit any practical difference; between 1.0% and 0.5% grade change, comfort criteria showed unacceptable performance for high speed tests; zero-length vertical curves were more likely to meet drainage grade requirements than were minimum design vertical curves; and accident studies did not reveal any apparent relationship to the type of vertical curve.

• Record URL:
  • https://library.ctr.utexas.edu/hostedpdfs/tti/2975-1.pdf
• Supplemental Notes:
  • Research study title: Evaluate the Conditions Which Would Permit the Use of a Vertical PI Without a Vertical Curve Being Necessary.
• Corporate Authors:

  Texas Transportation Institute

  Texas A&M University System, 1600 E Lamar Boulevard
  Arlington, TX  United States  76011

  Texas Department of Transportation

  Research and Technology Transfer Office, P.O. Box 5051
  Austin, TX  United States  78763-5051
• Authors:
  • Wooldridge, M D
  • Parham, A H
  • Nowlin, R L
• Publication Date: 1997-9

Language

• English

Media Info

• Features: Appendices; Figures; Photos; References; Tables;
• Pagination: 84 p.

Subject/Index Terms

• TRT Terms: Comfort; Crashes; Design speed; Drainage; Geometric curves; Slopes; Studies
• Uncontrolled Terms: Accident studies; Grade (Slope); Vertical curvature
• Subject Areas: Design; Highways; Hydraulics and Hydrology; Safety and Human Factors; I20: Design and Planning of Transport Infrastructure;

Filing Info

• Accession Number: 00748799
• Record Type: Publication
• Report/Paper Numbers: TX-98/2975-1,, Res Rept 2975-1,, TTI: 7-2975
• Contract Numbers: Study 7-2975
• Files: TRIS, ATRI, STATEDOT
• Created Date: May 22 1998 12:00AM