SECTION 1. Chapter 90 of the General Laws is hereby amended by striking out Section 17A, as appearing in the 2016 Official Edition, and inserting after the first paragraph of Chapter 81, Section 7C, the following:

Notwithstanding any general or special law to the contrary, the speed limit on a limited-access way, including the Massachusetts Turnpike, shall be determined by an engineering and safety study and by the eighty-fifth percentile speed of free-flowing traffic under ideal conditions of a section of limited-access way, rounded to the nearest multiple of five miles per hour. A speed limit established under this act shall not be posted at less than the fiftieth percentile speed of free-flowing traffic under optimal conditions on the fastest portion of the limited-access way segment for which the speed limit is being posted. If a limited-access way segment includes one or more features with a design speed that is lower than the speed limit determined under this section, advisory signs may be posted. Speed limits posted using a variable message sign may be adjusted to compensate for congestion, weather conditions, or any other temporary factor that has a bearing on a safe speed.