The AASHTO Green Book suggests flexibility for tradeoffs in lane and shoulder widths provided a minimum roadway width is achieved.
Source: A Guide for Achieving Flexibility in Highway Design p. 66
Published: 2004
From A Guide for Achieving Flexibility in Highway Design, 2004, by the American Association of State Highway and Transportation Officials, Washington, D.C. Used by permission. AASHTO publications may be purchased from that organization’s bookstore at 1-800-231-3475 or online at https://bookstore.transportation.org/.
