Route 2A begins at the rotary intersection with Route 2 at I-91 in Greenfield. It passes through downtown Greenfield before reconnecting to its parent route just west of the Greenfield-Gill town line. After a silent concurrency, Route 2A leaves Route 2 once more, passing through Orange and Athol. In Athol it passes the former northern terminus of Route 21, which was truncated to Belchertown after the creation of the Quabbin Reservoir. From Phillipston through Westminster, Route 2A weaves around its parent route, crossing it a total of six times with five exits of access off of Route 2. In Fitchburgthe road is shared with several other routes as it passes through the northern half of town. Once in Lunenburg it has another short concurrency with Route 13 just north of the former Whalom Park before crossing into Middlesex County at Shirley. In Shirley, Route 2A passes north of Fort Devens into Ayer, heading into Littleton and crossing I-495 at exit 30. It then turns south through Acton and into Concord before rejoining its parent route once more. As a silent concurrency, it passes south of the historic center of town and north of Walden Pond before splitting again. Route 2A then passes through the Minuteman National Historical Park along the Great Road, the route taken by British troops between the Battles of Lexington and Concord. It then leaves the park, intersecting with I-95/Route 128 at exit 30. The road passes south of Lexington's town center before winding into Arlington. In Arlington, the road begins a concurrency with U.S. Route 3 which eventually joins the route to Massachusetts Avenue. After US 3 leaves Mass Ave at Alewife Brook Parkway, Route 2A continues through the city ofCambridge, passing by Harvard Yard and through Harvard Square. Due to the one-way circulation patterns of the square, Route 2A follows Mass Ave in the westbound direction and a combination of Massachusetts Avenue, Brattle Street, and Mt. Auburn Street in the eastbound direction before rejoining Mass Ave east of Putnam Avenue. It then passes by the Massachusetts Institute of Technology. It intersects the junction of US 3 and Route 3 at Memorial Drive before crossing the Harvard Bridge and crossing into Boston, ending at Route 2 and Commonwealth Avenue.
Signage mistakes
In 2013, Route 2A signs were extended further into Boston through the Back Bay and South End neighborhoods along Massachusetts Avenue. This extension connected it with several additional numbered routes including the Massachusetts Turnpike by its junction with Boylston Street, Huntington Avenue, Tremont Street, and Melnea Cass Boulevard in Roxbury. Not only did neither the Massachusetts Department of Transportation nor the Boston Transportation Department, acknowledge that Route 2A had been extended, they denied knowing who put up the signs, indicating it was the action of an unknown organization. The Route 2A signs themselves had either wrong directional banners or are signed backwards, as it heads in a northwesterly direction towards Commonwealth Avenue beyond Tremont Street. On February 26, Boston television station, WFXT-TV aired an investigative reporting segment showing the incorrect signs and their attempt to track down the source. In the report, Boston transportation officials admitted they had paid a private firm, Jacobs Engineering, to manufacture and put up the signs through a wayfinding improvement grant. The signage errors were caused by problems with the plans developed by Jacobs that apparently were not checked for accuracy before they were approved for installation by the city. The city said they were going to take action against the firm to recoup moneys from Jacobs, and would work to fix the signs as soon as possible. Meanwhile, a MassDOT official reiterated that the eastern terminus of Route 2A is at the intersection of Massachusetts and Commonwealth Avenue and that crews would be removing the MA 2A signs further east. In the city's defense, they stated that they do not typically manufacture, install, or maintain signage pertaining to state entities, similar to an arrangement with the Massachusetts Bay Transportation Authority relating to bus stop signage within the city.
