The numbering system change is part of a 2009 FHWA mandate requiring exit numbers to match mile markers for national uniformity. Most states have completed the change; Massachusetts is one of three states not in compliance; non compliance could result in the withdrawal of federal funds, as explained in this video:
New Mass Exits maintains an interactive website that monitors the changes throughout the state, displaying the locations of the the new mileage-based exit numbers. You can also download a PDF explaining the exit renumbering project here.
To view new exit numbering on each corridor, click on the route number below:
According to MassDOT, the old exit numbers will be displayed along with new ones at key locations for a minimum of two years, the old signs will remain in place for two years, and exit number changes will now appear in navigation apps as well.
Stay up to date here.
Source: Massachusetts Department of Transportation
