Guidelines for Geometric Design of Low-Volume Roads - SECOND EDITION

Abstract

The guidelines presented in this document are intended for application in the design of low-volume roads, as defined above, including application in new construction of low-volume roads and in the improvement of existing low-volume roads.

The scope of the guidelines includes roads in both rural and urban areas.

These design guidelines enable designers for projects on low-volume roads to apply design criteria that are less restrictive than those generally used on higher volume roads.

Where the term higher volume roads is used in this document, this refers to roads with design volumes of more than 2,000 vehicles per day, which are outside the scope of these guidelines.

The risk assessment on which the guidelines are based shows that these less restrictive design criteria can be applied on low-volume roads without substantial effects on crash frequency and severity.

The guidelines discourage widening of lanes and shoulders, changes in horizontal and vertical alignment, and roadside improvements except in situations where such improvements are likely to provide substantial reductions in crash frequency or severity.

Thus, projects designed in accordance with these guidelines are less likely to negatively impact the environment, roadway and roadside aesthetics, existing development, historic and archeological sites, and endangered species.

In reviewing the geometric design for sections of existing roadway, designers should strive for consistency of design between that particular section and its adjoining roadway sections.

The potential effects of future development that may affect the traffic volume, vehicle mix, and presence of pedestrians or bicyclists on the roadway should also be considered.

These design guidelines are intended to encourage rational safety management practices on low-volume roads.

Expenditures for highway improvements are discouraged at sites where such improvements are likely to have little effect on crash frequency or severity, but are strongly encouraged at sites where crash patterns exist that can be corrected by a roadway or roadside improvement.

Designers are provided substantial flexibility to retain the existing roadway and roadside design, where that existing design is performing well, but are also provided flexibility to recommend improved designs, even designs that exceed the guidelines presented here, where needed to correct documented crash patterns or meet other agency goals.

The scope of these guidelines includes geometric design for new construction and for improvement of existing roads.

Geometric design criteria for new construction apply to construction of a new road where none existed before.

Projects on existing roads may involve reconstruction, resurfacing, rehabilitation, restoration, and other types of improvements.

These guidelines are limited in scope to geometric design issues and do not address the application of traffic control devices on low-volume roads.

For traffic control device guidance, see the Manual on Uniform Traffic Control Devices (8).