The Zakim Bridge, Boston, Massachusetts

Stand on the Charlestown side of the Charles River at dusk and look south, and the Zakim Bridge does something no other structure in Boston does: it frames the city. Two inverted-Y towers, 270 feet tall, rise out of the river's edge, and white stay-cables fan from them in a harp pattern to a deck ten lanes wide. At night the towers glow blue and the cables shine white, and the whole span reads as a gateway — which is exactly what it was designed to be.

Its full name is the Leonard P. Zakim Bunker Hill Memorial Bridge, and almost nobody calls it that. Bostonians call it "the Zakim," and Charlestown residents often call it the "Bunker Hill Bridge." It carries Interstate 93 and U.S. Route 1 across the Charles River between the North End side of Boston and Charlestown, connecting the Thomas P. "Tip" O'Neill Jr. Tunnel downtown with the elevated highway to the north. It is a highway bridge — there are no sidewalks on it, and you cannot walk across it — but it is also one of the most photographed structures in New England, the backdrop television networks reach for to establish that a story is taking place in Boston, and a fixture on postcards and souvenirs. It opened to traffic in 2003, which makes it the youngest landmark on the skyline it now defines.

The bridge is worth a visit precisely because you cannot walk on it. The experience of the Zakim is the experience of looking at it — from Paul Revere Park in Charlestown, from North Point Park across the river in Cambridge, from the curving pedestrian bridge that passes beneath it — and of standing underneath it, in a landscape of parks and public art that the Big Dig left behind. The bridge is the monument. The ground beneath it is the visit.

To understand the Zakim, you have to understand the hole it was built to fill. For half a century, Boston's downtown was cut in two by the Central Artery, an elevated six-lane highway that carried I-93 through the heart of the city on a rusting steel viaduct. By the 1980s the Artery was carrying far more traffic than it was designed for, and the city decided to bury it. The Central Artery/Tunnel Project — the Big Dig — put the highway underground in the Thomas P. "Tip" O'Neill Jr. Tunnel, tore down the elevated road, and opened the Rose Fitzgerald Kennedy Greenway on the land where the viaduct had stood. It was the largest highway construction project in the United States, commonly put at about $15 billion, and it remade the city's map.

The Zakim was the project's signature span: the northern gateway where the buried highway comes back to the surface and crosses the Charles. The old crossing, the Charlestown High Bridge — a steel truss bridge built in the 1950s — was deteriorating and too narrow for the traffic it carried, and the new bridge had to do something the old one never had: carry ten lanes of interstate highway across the river while threading between the Orange Line tunnel that runs beneath the riverbed, the commuter rail lines at North Station, and the dense neighborhoods on both banks. Construction ran from 1997 to 2003, and the towers were finished by the end of 1999. The bridge was built just upstream of the old span, which stayed in service until traffic moved over, and the High Bridge was demolished in the spring of 2004.

Before a single car crossed it, Bostonians got to walk it. On May 12, 2002 — Mother's Day — more than 200,000 people crossed the new span on foot in a public celebration, months before it opened to traffic. The bridge was dedicated in early October 2002 in a ceremony held on the deck itself, with members of Zakim's family and government officials in attendance, and Bruce Springsteen performing "Thunder Road." The northbound lanes opened on March 30, 2003; the southbound lanes followed on December 20, 2003, and the last two lanes opened in early 2005. The bridge cost a reported $105 million — a small fraction of the Big Dig's total, and the part of the project almost everyone agrees was money well spent.

The bridge's design is the work of Swiss bridge engineer Christian Menn, who conceived it in collaboration with bridge designer Miguel Rosales; the design was engineered by American civil engineer Ruchu Hsu with Parsons Brinckerhoff (now WSP USA), with Wallace Floyd Associates as lead architect and urban designer. It was, by one contemporary account, the first cable-stayed bridge in the United States with an asymmetrical, hybrid design — a structure shaped as much by what it had to avoid as by what it had to carry.

The numbers are the first thing to grasp. The bridge is 1,432 feet long and 183 feet wide — MassDOT calls it the widest cable-stayed bridge in the world — with a main span of 745 feet and 40 feet of clearance above the water. The two towers rise 270 feet, and eight lanes of I-93 pass through the legs of the towers while two additional lanes are cantilevered outside the cables, carrying northbound traffic from the Sumner Tunnel and the North End on-ramp; those lanes merge with the main highway north of the bridge. More than 200,000 vehicles cross it on a typical day.

The towers are the design's signature. Each is an inverted Y — sometimes described as a wishbone — in reinforced concrete, and the top of each pylon is shaped like an obelisk. That is not decoration. The obelisk tops are a deliberate reference to the Bunker Hill Monument, the 221-foot granite obelisk that stands on Breed's Hill in Charlestown, a short walk from where the bridge lands. The bridge is, in effect, a modern answer to the monument: the same shape, rendered in concrete and steel and light, marking the same neighborhood's place in the city's story. The connection is also in the name. The bridge's full name commemorates both Leonard P. Zakim and the Battle of Bunker Hill, fought on June 17, 1775, on the ground the bridge now overlooks.

The cables are the second half of the design. The Zakim is a cable-stayed bridge in a harp configuration, with the stays running in parallel lines from the towers to the deck rather than fanning out from a single point — and with a detail that was unusual at the time: each strand is carried through its pylon in a cradle, rather than anchored to it. The white cables against the blue-lit towers are the image everyone carries away, and at the right hour — late afternoon in winter, when the sun hits the stays at a low angle — the whole span seems to glow.

The engineering had to solve a problem you cannot see. The MBTA Orange Line's Haymarket North Extension tunnel, built in 1975, lies directly beneath the bridge, and the bridge's foundations had to be placed without disturbing it. The result is a structure that looks effortless and was anything but: a ten-lane highway balanced over a subway tunnel, a river, and a rail yard, on a footprint that had to thread between buildings that were already there.

The bridge is named for Leonard Paul Zakim (1953–1999), known to everyone as Lenny — a Boston civil rights leader whose life's work was, in his own phrase, "building bridges between peoples." Zakim grew up in New Jersey, came to Boston for law school, and in 1979 was hired by the Anti-Defamation League as its New England civil rights director; in 1984 he became the ADL's New England director, a post he held until his death. He spent two decades working to bring together Boston's Jewish, Black, and Catholic communities in some of the city's most racially charged years, and in 1985 he founded the ADL's World of Difference Institute, a program to combat racism, antisemitism, prejudice, and bigotry in schools. He also founded the Team Harmony Foundation, which brought young people of different backgrounds together. He died on December 2, 1999, at 46, after a five-year battle with bone-marrow cancer — just as the bridge that would bear his name was rising over the river.

The naming was not uncontested. Governor A. Paul Cellucci had originally sought to call the span the "Freedom Bridge." In 2000, shortly after Zakim's death, local clergy and religious leaders — including Cardinal Bernard Law — asked that it be named for Zakim instead, and the "Bunker Hill" half of the name was added because the bridge lands in Charlestown, in the shadow of the monument. The choice has proved itself. As the historian's account of the naming puts it, rarely is a choice as fitting as naming a bridge for a man whose life's work was fostering connections among people — and the bridge's dedication made the point in the plainest terms. Introducing "Thunder Road" at the ceremony, Bruce Springsteen said of Zakim that he was "one of those people whose intensity, inner spirit you could feel even when he was very ill," and that "we honor his memory obviously not with this beautiful bridge, very lovely, but by continuing on in his fight for social justice."

The Zakim is a different bridge after dark, and the lighting is part of the design, not an afterthought. Bridge architect Miguel Rosales described the intent plainly: "the bridge is supposed to have the feel of a regal entry to Boston, the towers bathed in blue, the cables highlighted in gleaming white." The original lighting used metal-halide fixtures, which by 2012 had grown dim; that December, MassDOT relit the towers with a Philips Color Kinetics LED system, unveiled in December 2012, which cut the lighting's energy use by more than 80 percent and — crucially — made the colors changeable at the touch of a button.

Since then the bridge has become the city's billboard in light. It glows green for the Celtics in the playoffs and on St. Patrick's Day, pink during Breast Cancer Awareness Month, red, white, and blue for the Patriots, and in the colors of causes and commemorations through the year — MassDOT publishes a lighting calendar and takes requests for single- or multi-color lightings on the Zakim and the city's other lit bridges. The default, though, is the blue and white Rosales intended: the towers bathed in blue, the cables gleaming white, the whole span reflected in the Charles. The best time to see it is the blue hour, just after sunset, when the sky is still light enough to read the towers' shape and the lights have just come on.

The most surprising thing about the Zakim is what happened underneath it. Placing the bridge's footings required environmental permits to relocate areas of open water surface, changing the contour of the Charles River shoreline — and the landscape design and environmental mitigation that followed created a new and accessible public landscape beneath the deck, designed by Carol R. Johnson Associates. It is one of the best pieces of urban repair the Big Dig produced: land that had been inaccessible beneath highway ramps became parkland, opened in 2012, now managed by the Department of Conservation and Recreation.

The centerpiece is Five Beacons for the Lost Half Mile, a series of perforated stainless-steel sculptural volumes lit from within, by artist Ross Miller, which guide pedestrians along the north bank of the Charles through the vast outdoor room formed by the highway above. The beacons shift color — a blue phase, an orange phase — and they turn a space that could have been a dead zone under a highway into a place people walk through on purpose. The landscape connects, via the North Bank Bridge — a curving pedestrian and cycling bridge that passes directly beneath the Zakim — to North Point Park in Cambridge, and from there to Paul Revere Park in Charlestown, the Charles River Dam, and the Charlestown Navy Yard. The North Bank Bridge is a link in the Charles River Bike Path and a segment of both the Mass Central Rail Trail and the East Coast Greenway, which means the ground beneath the Zakim is part of a walking and cycling route that runs, in pieces, from Boston Harbor deep into the state.

Do not try to walk across the Zakim. There are no sidewalks on the bridge, and it is a ten-lane interstate highway; the only way across it is in a vehicle. The bridge rewards viewers, not crossers, and the viewpoints are all at its feet.

Start in Paul Revere Park, in Charlestown, which runs between the Freedom Trail on North Washington Street and the bridge itself, with a large oval lawn and a playground; the towers rise above the park's eastern end, and the bridge's silhouette from the park is one of the classic Boston photographs. From there, cross the North Bank Bridge — the pedestrian bridge that curls beneath the Zakim — to North Point Park on the Cambridge side, an 8.5-acre riverside park with a low angle on the cables and the towers, wide views of the Boston skyline, and a playground and spray deck. The view from below, looking up from the North Bank Bridge, gives a sense of the structure's scale that no photograph from a car window can match. For a skyline shot with the towers in the foreground, the riverfront near North Station and TD Garden is the easy option, and photographers also work from the Museum of Science's back decks and, with a telephoto lens, from the Longfellow Bridge, compressing the Zakim against the downtown skyline.

If you climb the Bunker Hill Monument — the granite obelisk the bridge's towers echo — you can look back from Breed's Hill toward the river and see the bridge in its setting, the modern obelisks answering the old one. The pairing is the point of the design, and it reads best from the monument's hill.

Getting there is easy. Take the MBTA Green or Orange Line to North Station and walk to the riverfront, or the Orange Line to Community College for the Charlestown side and Paul Revere Park; the Green Line's Science Park station serves North Point Park. The bridge itself is free to drive across and free to look at — it is a highway, not an attraction with a gate — and the parks beneath it are public and free to enter, typically open during daylight hours. Come at the blue hour if you can: the towers turn blue, the cables turn white, and the youngest icon on the Boston skyline looks like it has always been there.

Address: Leonard P. Zakim Bunker Hill Memorial Bridge, carrying I-93/US 1 over the Charles River between the North End and Charlestown, Boston, MA. The bridge itself has no street address; the map pin is at the center of the span (42.3689, -71.0633).

Transit: MBTA Green or Orange Line to North Station, then walk to the riverfront; Orange Line to Community College for the Charlestown side and Paul Revere Park; Green Line (E branch) to Science Park for North Point Park.

Admission: None — the Zakim is a highway bridge, free to drive across and free to view. The parks beneath and beside it (Paul Revere Park, North Point Park) are public and free to enter, typically open during daylight hours; no hours are stated as fact here because they were not verified against an official source in this run.

Best viewpoints: Paul Revere Park in Charlestown (towers rising above the park's eastern end; the classic silhouette shot); the North Bank Bridge beneath the Zakim (looking up at the deck and cables); North Point Park in Cambridge (low angle on the cables, skyline views); the riverfront near North Station and TD Garden (skyline shot with the towers in the foreground); the Museum of Science back decks; the Longfellow Bridge with a telephoto lens; and the top of the Bunker Hill Monument, looking back toward the bridge.

Best timing: The blue hour just after sunset, when the towers glow blue and the cables shine white; late afternoon in winter, when low sun strikes the white stay-cables. Do not attempt to photograph while driving — use the parks.

Note: There is no pedestrian crossing on the bridge itself. Walkers and cyclists cross the river on the North Bank Bridge, which passes beneath the Zakim.