How much latitude does a Town have in "adjusting" the width of Main Street as part of a comprehensive plan?

There are standards for highways (highlighted in a Tech Tip on highway standards linked below) including those prepared by AASHTO and the NYSDOT. However, there is quite a bit of flexibility if designs are made using the concepts of context sensitive design. As a starting point, the Local Roads Program's workbook on Complete Streets and Highway Standards for Low-Volume Roads in New York State are good references.

Resources

Context sensitive solutions (CSS) Federal Highway Administration (FHWA)

Complete Streets: Planning Safer Communities for Bicyclists and Pedestrians (pdf)

Highway Standards for Low-Volume Roads in New York State (pdf)

Guidelines and Standards for Classifying & Managing Roads & Streets (pdf)