Search fhwa.dot.gov

General Guidelines for the Geometrics of Bridge Design

This historic wrought iron camelback truss is one of the few remaining in the country.  It has been preserved by moving it to a new location, where it now serves as a footbridge. (Baraboo, WI) "Bridges and other related major structures play an important role in defining the manner in which a highway affects the aesthetic, scenic, historic, and cultural resources of the corridor within which it is located....The geometric criteria in the AASHTO Green Book for new or replacement bridges deal primarily with the width of the bridge deck and its relationship to approach roads. Early design coordination is important when establishing the width of a new or replacement bridge and in determining its horizontal and vertical alinement. Road engineers, architects, and landscape architects, as well as members of the community, can provide input to help the bridge designer determine the appropriate geometric dimensions and overall appearance of the bridge....In addition to determining the width of the travelway, a bridge designer must consider the need for pedestrian and non-vehicular traffic over the bridge and the most appropriate method for accommodating it." BRIDGES AND OTHER MAJOR STRUCTURES

BACKGROUND

Bridges and other related major structures play an important role in defining the manner in which a highway affects the aesthetic, scenic, historic, and cultural resources of the corridor within which it is located. Indeed, some of the distinguishing features of a number of major cities are their bridges. When one thinks of San Francisco, one of the first images that comes to mind is the Golden Gate Bridge. Smaller structures have a visual impact as well, such as the Manchester Street Bridge in Baraboo, WI, shown in the attached image.

GENERAL GUIDELINES FOR THE GEOMETRICS OF BRIDGE DESIGN

The geometric criteria in the AASHTO Green Book for new or replacement bridges deal primarily with the width of the bridge deck and its relationship to approach roads. Early design coordination is important when establishing the width of a new or replacement bridge and in determining its horizontal and vertical alinement. Road engineers, architects, and landscape architects, as well as members of the community, can provide input to help the bridge designer determine the appropriate geometric dimensions and overall appearance of the bridge. The AASHTO Green Book presents a range of options for traveled-way widths for bridges with a span of less than 30 m, depending on functional classification and average daily traffic, as illustrated in the following tables.

On urban collectors and arterials, the AASHTO Green Book recommends that the minimum clear width for new bridges be the same as the curb-to-curb width of the approach street.

In addition to determining the width of the travelway, a bridge designer must consider the need for pedestrian and nonvehicular traffic over the bridge and the most appropriate method for accommodating it. This could include a wide shoulder, a raised sidewalk, or both. If sidewalks are on the approach road, continuity of the sidewalk over the bridge is important.

For existing bridges that do not meet the criteria for travelway width, the AASHTO Green Book recognizes that those that tolerably meet the criteria may be retained. It identifies some of the factors in considering the retention of existing bridges, including モthe aesthetic value and the historical significance attached to famous structures, covered bridges, and stone archesヤ (p. 423). Because of this, AASHTO has criteria for minimum roadway widths and minimum structural capacities for bridges that are to remain in place. It is important to consider this option for each aesthetically and historically significant bridge on a case-by-case basis, before deciding to demolish and replace it.


Related Content:

Feedback, questions, comments, or problems?
email info@contextsensitivesolutions.org

Copyright © 2005 Context Sensitive Solutions.org. All rights reserved.
About Us | Site Map | Privacy Policy

United States Department of Transportation - logo
Privacy Policy | Freedom of Information Act (FOIA) | Accessibility | Web Policies & Notices | No Fear Act | Report Waste, Fraud and Abuse | U.S. DOT Home |
USA.gov | WhiteHouse.gov

Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000