Upon turning northward, the highway is known as the Southeast Expressway, passing through Quincy and Milton before crossing into the city of Boston over the Neponset River.

After the Massachusetts Avenue connector exit, the highway officially becomes the John F. Fitzgerald Expressway, also known as the Central Artery, and passes beneath Downtown Boston.

After the massive interchange, motorists use the O'Neill Tunnel to travel underneath the city and then use the Leonard P. Zakim Bunker Hill Memorial Bridge to cross the Charles River.

Farther north, in Andover, I-93 meets I-495, providing access to Worcester to the southwest and New Hampshire's Seacoast Region to the northeast.

Several exits were removed from I-93 to address traffic problems in addition to converting the Central Artery from 6 to 8 to 10 lanes, by reducing the combined number of on- and offramps from 27 to 14.

I-93 in New Hampshire is also notable for having state liquor stores serve as rest areas, which are passed just after the toll plaza, traveling north.

I-93 maintains three lanes of traffic in each direction until the junction with I-89, then is a four-lane freeway through most of its journey northward, with the only exception being the Franconia Notch section.

In the state capital of Concord, I-393 heads directly east (cosigned with eastbound US 4 and US 202), providing another route to the Seacoast Region.

Beyond Franconia Notch State Park, US 3 heads northeastward through the Great North Woods Region, while I-93 runs to the northwest.

In 2013, a bill was signed by governor Maggie Hassan to raise the speed limit on I-93 to 70 mph (110 km/h) from milemarker 45 to the Vermont border, with the exception of the Franconia Notch Parkway.

[11] On August 21, 1969, a train of three runaway locomotives burst out of what is now Cabot Yard, across Frontage Road, and blocked the northbound side of the highway.

Because of the public outcry, Governor John A. Volpe ordered the southern half of the highway redesigned so that it was underground; this section became known as the Dewey Square Tunnel.

With the cancelation of the highway projects leading into the city in 1972 by Governor Francis Sargent, the Central Artery gained the designation of I-93 in 1974.

The outcry eventually led to the replacement of Scheme Z with a newer, more sleek cable-stayed bridge and complementing exit for Cambridge, increasing the cost even more.

In Downtown Boston, I-93 is made up of the O'Neill Tunnel and Leonard P. Zakim Bunker Hill Memorial Bridge, which spans the Charles River.

The former route of the above-ground Artery, so named "the other Green Monster" by Mayor Thomas Menino, was replaced mostly by open space known formally as the Rose Fitzgerald Kennedy Greenway.

The Massachusetts State Police has expressed displeasure with this arrangement, citing that traffic in the breakdown lanes interferes with the ability of emergency vehicles to respond to accidents.

[citation needed] In August 2010, in Medford, a 25-by-7-foot (7.6 m × 2.1 m) section of bridge deck on the northbound side partially collapsed due to age-related structural fatigue.

By 1956, the two states had drawn up new plans for I-93 to the east, bypassing the tolled Everett Turnpike from Manchester southward along a new alignment, known as the "Northern Expressway" in Massachusetts and crossing into New Hampshire in Salem.

This left a gap in I-93, as traffic was directed along NH 101 West and the Everett Turnpike, while the southern segment of I-93 continued on and ended in a stub at exit 7.

[citation needed] Begun in 2006 and continuing until 2021, the portion between the state border and the I-293 southern terminus was widened to eight lanes; this necessitated the rebuilding and/or relocation of several interchanges.

An additional 2010 proposal to upgrade Route 24, running southwards from I-93 exit 4 in Randolph to I-195 near Fall River, has also been put off due to studies showing the cost of the project being very high.

The Conservation Law Foundation (CLF) filed a lawsuit in February 2006, hoping to force any expansion plans in the area to include the restoration of commuter rail service between Manchester and Boston.

The whole set of projects were eventually allowed to move forward following an agreement between the state and the CLF that removed the group's opposition to construction which does not pose a threat to the environment.

[30] As part of the 2009 stimulus package, New Hampshire was set to receive several million dollars in highway construction funds.

In addition, all five interchanges along this length would be upgraded to accommodate larger amounts of traffic, including the replacement of many aging bridges.

[30] According to plans filed by the state with USDOT, the project was scheduled to run from 2009 through 2016, with work starting at the Massachusetts line and moving northward to Manchester.

[32] As a way to help defray the costs of the expansion, in early 2010, NHDOT made a formal request to the Federal Highway Administration to add tolls to I-93 at the Massachusetts–New Hampshire border.

The new toll facility was to be located in Salem, approximately 0.5 miles (0.8 km) north of the state line, and would cost travelers $2.00 per vehicle.

The new rest areas feature a 14-pump Irving Oil gas station, a new New Hampshire liquor and wine outlet, and a few restaurants and shops.