Safety Effects of Using Narrow Lanes and Shoulder-Use Lanes to Increase the Capacity of Urban Freeways

2005PDFTech Reporthttps://www.fhwa.dot.gov/publications/research/safety/05001/05001.pdfhttps://www.fhwa.dot.gov/publications/research/safety/05001/FHWA-HRT-05-001Traffic volumeHighway capacityFreewaysUnited StatesUnited States. Federal Highway Administration. Office of Research, Development, and TechnologyUnited States. Federal Highway Administration. Office of Research, Development, and TechnologyTurner-Fairbank Highway Research CenterTan, CarolFederal Highway AdministrationAs traffic volumes grow on urban freeways, highway agencies face an ongoing challenge to maintain efficient traffic operations and acceptable levels of service. Increasing the capacity of a freeway by adding a lane can be difficult and expensive if it involves widening the existing roadbed, regrading roadside areas, and/or acquiring additional right-of-way. A number of highway agencies, however, have implemented projects in which a travel lane is added on an urban freeway by restriping the traveled way with narrower lanes, converting all or part of the shoulder to a travel lane, or a combination of both. The traffic operational benefits of such conversions are immediate and obvious, but the safety effects are uncertain. This study addresses these safety effects.78