The results of this research have been published as NCHRP Report 369, Use of Shoulders and Narrow Lanes to Increase Freeway Capacity.

Increasing traffic congestion, coupled with limited resources to build new freeways, has created a need for additional capacity on existing freeways. Frequently, this can be accomplished by adding lanes through the use of shoulders both as a stand-alone strategy or in conjunction with reduced lane widths. This approach offers a lower cost alternative, with minimal community impacts and can be implemented more quickly than widening the freeway to add lanes. Projects of this type have been implemented in several states and are proposed in others.

The objectives of this project were (1) to investigate the trade-offs among facility design, traffic performance, safety, enforcement, system operations and maintenance impacts; (2) to develop a methodology for the evaluation of alternative applications; and (3) to provide recommended design guidelines for these strategies.