Standard, Guidance, Option and Support
In the MUTCD, the terms Shall, Should, and May have gone from being primary words to being used to modifiers within different sections. The new big three terms are Standard, Guidance, and Option.
Standards must be followed and are mandatory. No discretion in following them is allowed. Items included as a standard usually use the word “shall” to describe what is to be done.
Guidance sections are recommendations and are normally followed if possible. Items listed as guidance usually use the word “should” to describe the critical items. Deviation from guidance provisions is permissible if there are valid reasons to deviate. The reasons should be documented and filed for future reference.
Option sections are included to alert the user of the MUTCD that something “may” be done. No requirement is intended. Items marked as options usually use the word “may.”
In addition to Standards, Guidance, and Options, the MUTCD contains additional information and background details that can be very useful when deciding when and where to place a traffic control device. This background information is usually included in a support section.