Skip to main content

Design Guidelines for Horizontal Sightline Offsets

View Cover

Overview

Contributors

Description

The distance between the driver’s line of sight along the roadway ahead on a horizontal curve and a sight obstruction on the inside of the curve is known as the horizontal sightline offset (HSO). Highway agencies can use NCHRP Research Report 910: Design Guidelines for Horizontal Sightline Offsets as guidance to address the types of sight distance restrictions that are most likely to be encountered on specific roadway types.

The relationship between stopping sight distance (SSD) and the frequency and severity of crashes has been difficult to quantify because the role of SSD in reducing crashes is highly situational. The design criteria for the horizontal component of SSD in what is known as AASHTO's Green Book are based on the maximum sightline offset that may be needed at any point along a curve with a given radius, which doesn't cover all possible situations.

Designers compensate for the limitations on driver sight distance in various ways, including: accepting shorter sightlines, lowering design speed, increasing shoulder width, or providing additional signage. There are advantages and disadvantages to the trade-offs; as a result, many highway agencies have used the design exception process to address the trade-offs for sight distance in such situations.

This project conducted research to evaluate these situations and determine what criteria or mitigation will provide acceptable solutions when impaired horizontal sightline offsets are encountered. The project includes a tool (an Excel spreadsheet) that may be used to calculate sight distance.

Topics

Suggested Citation

National Academies of Sciences, Engineering, and Medicine. 2019. Design Guidelines for Horizontal Sightline Offsets. Washington, DC: The National Academies Press. https://doi.org/10.17226/25537.

Import this citation to:

Publication Info

114 pages | 8.5 x 11
DOI: https://doi.org/10.17226/25537
Contents
Resources

Links

Rights

Copyright Information

The National Academies Press and the Transportation Research Board have partnered with Copyright Clearance Center to offer a variety of options for reusing our content. You may request permission to:

  • Republish or display in another publication, presentation, or other media
  • Use in print or electronic course materials and dissertations
  • Share electronically via secure intranet or extranet
  • And more

For most Academic and Educational uses no royalties will be charged although you are required to obtain a license and comply with the license terms and conditions.

Click here to obtain permission for Design Guidelines for Horizontal Sightline Offsets.

Translation and Other Rights

For information on how to request permission to translate our work and for any other rights related query please click here.

Copyright.com Customer Service

For questions about using the Copyright.com service, please contact:

Copyright Clearance Center
22 Rosewood Drive
Danvers, MA 01923
Tel (toll free): 855/239-3415 (select option 1)
E-mail: info@copyright.com
Web: https://www.copyright.com
Stats

Loading stats for Design Guidelines for Horizontal Sightline Offsets...