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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Public Roads - January/February 2013

January/February 2013
Issue No:
Vol. 76 No. 4
Publication Number:
Table of Contents

From Milepost to Milestone: Innovative Mitigation

by Kevin M. Bartoy

A one-of-a-kind information center in downtown Seattle helps Washington State alleviate a new tunnel's impact on a historic district.

The Alaskan Way Viaduct, shown here in an aerial photograph, has spanned Seattle’s waterfront for more than half a century. Upon completion of the S.R. 99 tunnel, the viaduct will be demolished, opening up 26 city blocks of new public space along the waterfront.

What happens when the world's largest diameter bored tunnel meets Seattle's oldest neighborhood? For the Federal Highway Administration (FHWA) and Washington State Department of Transportation (WSDOT), this major construction project in downtown Seattle afforded an opportunity to educate the public about state-of-the-art tunnel engineering and 20,000 years of the region's history.

Since the 1950s, the Alaskan Way Viaduct has served as a bypass for motorists traveling on State Route (S.R.) 99 through Seattle. When one of the largest recorded earthquakes in the State's history rocked Puget Sound in 2001, causing the viaduct to settle as much as 5.5 inches (12.7 centimeters) in some areas, transportation officials realized that the time had come to replace the aging structure. The chosen solution, a tunnel, would place the highway beneath the city, reopening the waterfront area for other uses, but bringing major construction activities to Seattle's Pioneer Square—Skid Road Historic District.

Through the consultation process to comply with Section 106 of the National Historic Preservation Act, WSDOT and FHWA heard loud and clear the concerns of historic preservationists, community advocates, and business owners. Many feared that having a major construction project on the edge of a nationally designated historic district would drive away tourists and customers visiting businesses in Seattle's first neighborhood. If businesses failed, the historic fabric of the neighborhood might well be affected, as building owners could no longer afford maintenance and upkeep of the century-old brick buildings that define Pioneer Square.

To help mitigate the effects of the tunnel construction on the historic district, the Washington State Department of Transportation created the Milepost 31 information center in this storefront to attract visitors to the neighborhood.

To mitigate potential adverse effects on the neighborhood, as part of a Section 106 memorandum of agreement, FHWA and WSDOT committed to opening an information center in the heart of the neighborhood. According to the agreement, the goal of the center is to draw visitors to Pioneer Square during construction and educate them about the past, present, and future of the neighborhood, highlighting the area's unique historical and archaeological features as well as engineering aspects of the S.R. 99 tunnel project, otherwise known as the Alaskan Way Viaduct Replacement project. The center's name, Milepost 31, refers to the milepost on S.R. 99 where the tunnel will begin to travel under Pioneer Square and, thus, where the neighborhood's future meets its past.

The Tunneling Technology

The S.R. 99 project is at the forefront of tunneling technology. At 57.5 feet (17.5-meters) in diameter -- roughly as tall as a five-story building -- the project's tunnel-boring machine is currently the world's largest. Crews first assembled the machine in Japan. Once completed, the machine was tested, taken apart, and barged to Seattle in more than 40 pieces and reassembled in an 80-foot (24-meter)-deep pit. Tunneling is scheduled to start the summer of 2013. Completion is expected in 2015.

Tunneling beneath Seattle will minimize closure of the highway during construction. Crews will constantly monitor ground conditions as they drive the machine forward. Safety measures will begin even before tunneling starts, when some 160 buildings above the tunnel route will be examined and fitted with monitoring equipment that enables crews to detect even the slightest movement. Buildings and other structures that are thought to be sensitive will be stabilized prior to tunneling.

"Milepost 31 is an example of our innovative approach to delivering projects," says Linea Laird, program administrator for WSDOT's Alaskan Way Viaduct Replacement project. "We took a federally mandated requirement -- that the agency take into account the effects of the project on historic properties -- and created an opportunity to enhance the Pioneer Square—Skid Road Historic District and the Alaskan Way Viaduct Replacement [project]. Milepost 31 is a unique project information center that will bring more people into the district and support the economic viability of this historic neighborhood."

Here's the story of how the Milepost 31 information center came to be.

Replacing the Alaskan Way Viaduct

Flanked by Elliott Bay to the west and Lake Washington to the east, Seattle's geography has always posed a transportation challenge for travelers trying to navigate the city's hourglass shape from north to south. As early as the 1910s, Seattleites sought a north-south bypass route through the city's central business district. However, it was not until the 1930s that engineers from the State and city conceived of an elevated roadway along Seattle's waterfront that would eventually become part of the mainline of U.S. 99, one of the first highways on the west coast connecting Canada and Mexico. Seattle's elevated road, the Alaskan Way Viaduct, was constructed in sections from 1949 to 1953. It provided an important bypass through downtown and, through the second half of the 20th century, became a recognizable symbol of the city's waterfront.

This cross section shows the layout of the bored tunnel.

A local newspaper of the day described the completed Alaskan Way Viaduct as "a royal necklace across the bosom of the Queen City of the Pacific Northwest." Many Seattleites extolled the vista of Elliott Bay and the Olympic Mountains afforded by a ride across the viaduct's upper deck. However, some perceived the viaduct to be an impediment to the revitalization of Seattle's waterfront, forming a barrier between the city and its beautiful harbor.

Nevertheless, the importance of the elevated roadway to the movement of people and goods through the city meant that calls for removing the viaduct fell short of mobilizing action. That remained true until February 28, 2001, when one of the largest earthquakes in the State's history rumbled through town.

Measuring 6.8 on the Richter scale and lasting approximately 45 seconds, the Nisqually earthquake provided a dramatic reminder that Seattle's aging infrastructure was at risk of catastrophic failure in this seismically active region. The viaduct, built on timber piles driven into former tidal flats and beaches, was stabilized and made safe for continued use. Still, local, State, and Federal officials realized that its replacement was no longer just about revitalizing the waterfront. Now it was a priority for public safety.

Over the decade from 2001 to 2011, FHWA, WSDOT, and the city of Seattle studied more than 75 design alternatives, produced 4 environmental documents under the National Environmental Policy Act, received more than 3,000 public comments, held 790 community briefings, and acted on the results of 2 public votes. Then, on August 22, 2011, FHWA signed a record of decision that concluded the environmental process by selecting the design alternative to replace the Alaskan Way Viaduct with a tunnel. Along with the selected contractor, Seattle Tunnel Partners, FHWA and WSDOT now are constructing the world's largest diameter bored tunnel, which will mine a subterranean path underneath downtown Seattle. When completed, the 1.7-mile (2.7-kilometer), 57.5-foot (17.5-meter)-diameter tunnel will carry two lanes of northbound and two lanes of southbound traffic under the city.

This tunnel bypass had been proposed in the 1940s by the modernist architect Paul Thiry as an early alternative to the viaduct. Thiry feared that the elevated structure would create slum conditions and bring blight to a waterfront that he felt was a tremendous asset. Now, more than 65 years after Thiry called the viaduct "a horrible thing to do to the city," a tunnel will usher in the revitalization of Seattle's waterfront and reconnect the city with its harbor.

Tunneling Into History

The S.R. 99 tunnel starts where the first settlements in Seattle began, at the southern edge of Pioneer Square, an area known in 1852 as Duwamps. The neighborhood was the young city's first commercial and residential center. Even before Europeans and Americans arrived, the area was a hub of activity for local and regional Native American tribes, and it remains a sacred place for descendants of those peoples today.

In its heyday, Pioneer Square mixed glamour and commerce with squalor and social ills. Alongside burgeoning businesses were thriving brothels, gambling parlors, and opium dens. When the legitimate businesses moved out, the illegitimate ones remained. As the city grew, the neighborhood became more well known as "Skid Row," a term likely coined in Pioneer Square as a mispronunciation of Skid Road, which was the informal name given to one of the primary streets in the neighborhood that was used to skid logs from the hills down to the mills. The deterioration of the neighborhood was exacerbated as the business district moved north and residents exited to the suburbs. However, through the benign neglect of many landlords, the neighborhood avoided redevelopment and retained its historic character throughout much of the 20th century.

Completed in 1891, the Pioneer Building in the center of the historic district is a vivid example of the Richardsonian Romanesque architectural style and the brick and stone construction that exemplifies Pioneer Square

In the 1960s, city officials began planning a ring road around downtown that would have required the demolition of many historic buildings in this area. Local advocates for historic preservation, such as Ralph Anderson and Victor Steinbrueck, recognized that the unique character of the buildings in the district still evoked the city's colorful past. Although the area had suffered some deterioration, advocates felt it still retained the integrity of a significant place. In 1970, a grassroots movement led to the neighborhood's designation as the Pioneer Square-Skid Road national historic district, one of the earliest in the country listed on the National Register of Historic Places. In that same year, the city established Pioneer Square as its first preservation district.

Visitors entering Milepost 31 see, from left to right, an information desk, soil core towers, and, in the background, a large wall mural portraying what the tunnel will look like to motorists. The ceiling is a simulation representing a tunnel's roof.

Today, Pioneer Square is defined by its beautiful brick and sandstone buildings constructed primarily in the Richardsonian Romanesque style. The buildings are remnants of the rebuilding of Seattle following the devastating Great Fire of 1889, which burned about 30 blocks of businesses and residences, many of the city's wharves, and its rail terminals. After the fire, the mayor and city council passed an ordinance that required all new buildings to be made of fire-resistant brick and stone. With 131 buildings, sites, structures, and objects dating from 1889 to 1931, the Pioneer Square-Skid Road Historic District is one of the Nation's best preserved districts from the Victorian Era.

Building a Future For the Past

To comply with the National Historic Preservation Act (Section 106), WSDOT and FHWA consulted a variety of stakeholders, including the Washington State Historic Preservation Officer, local governments, preservation and community advocates, building and business owners, and eight federally recognized Native American tribal governments. The Section 106 consulting parties were primarily concerned with retaining the physical integrity of historic buildings and the economic vitality of the neighborhood, particularly during the construction activities.

With regard to the historic buildings, WSDOT and FHWA committed to monitoring closely the direct effects of construction on the built infrastructure throughout the project's timeline. Addressing stakeholder concerns about impacts on economic vitality, however, posed a greater challenge. Pioneer Square is a neighborhood in the early stages of revitalization, an ongoing process bogged down by the hardships of the economic recession. Evaluating potential indirect adverse effects on the historic district would be difficult, but even more challenging would be developing mitigation measures to ensure the vitality and viability of the struggling neighborhood.

During the consultation process, representatives from the Washington State Department of Archaeology and Historic Preservation, the city of Seattle, and the nonprofit Alliance for Pioneer Square suggested that transportation officials direct funding toward marketing activities to entice visitors to Pioneer Square during construction. Taking this idea a step further, the transportation agencies and the consulting parties conceived of a brick-and-mortar destination that would give individuals a reason to visit the neighborhood. This destination would not only highlight the history of the neighborhood, but also would showcase history in the making by educating visitors on the new tunnel being bored under Pioneer Square.

Milepost 31's Exhibits

On December 1, 2011, less than 6 months after conception of the idea of a project information center, Milepost 31 opened at 211 First Avenue South, a former retail space in Pioneer Square. Employees of WSDOT staff the center Tuesday through Saturday, 11 a.m. to 5 p.m., with variable hours during large events in the neighborhood; admission is free.

"As the first center of its kind for WSDOT, Milepost 31 is a unique outlet that puts a major transportation project in context with the rich history of an affected neighborhood," says Laird. "It serves as a model for the use of creative mitigation to fulfill an agency's obligation to address the effects of its project on historic properties."

As with the tunnel itself, Milepost 31 is an ambitious project. Telling the story well required a collaborative effort. To bring the project to life, WSDOT worked closely with the contractor and Alliance for Pioneer Square; Burke Museum of Natural History and Culture and its Waterlines Project;; the Klondike Gold Rush National Historical Park; and the Suquamish, Muckleshoot Indian, Tulalip, Snoqualmie, and Puyallup tribes.

Milepost 31 contains four primary exhibits:

  • You Are Here -- A welcome area familiarizing visitors with the neighborhood and its history
  • Moving Land -- The natural and cultural history of Seattle's "engineered" landscape
  • Moving People -- The history of transportation in Seattle
  • Moving Forward -- Bored tunneling and the S.R. 99 Tunnel Project, where engineering and transportation come together in Pioneer Square

Upon entering the You Are Here exhibit, visitors see a sword fern icon that was chosen in consultation with the Muckleshoot Indian Tribe, who relayed a Coast Salish tradition that the sword fern represents one of the oldest teachers and keepers of knowledge. The icon is used throughout the exhibits.

You Are Here is designed to provide a variety of first-person perspectives on Pioneer Square over time. Personalities from the past through the present offer individual perspectives on the neighborhood and why it was (and still is) important. Featured individuals tell of their own role in Seattle's story through text on display panels:

  • Native History (Djidjila'letch, "little crossing over place," is the indigenous name for the location that became Pioneer Square): Chief Seattle, after whom the city was named, gives his perspective through an orator. Among the Coast Salish peoples, it was common practice for individuals of great importance to speak through an orator.
  • Early Exploration (Piner's Point): Charles Wilkes tells of leading an expedition in 1841 to survey Puget Sound and naming this area after Thomas Piner, a member of his expedition.
  • The Founding of Seattle (Seattle, or Duwamps): The speaker is Sarah Yesler, who was the city's first librarian and the wife of a former Seattle mayor.
  • Flourishing Pioneer Square: Here the speaker is William Grose, one of Seattle's first African American pioneers.
  • The Decline of Pioneer Square: The featured speaker is Sam Israel, who owned and preserved many of Pioneer Square's historic buildings.
  • The Revitalization of Pioneer Square: The speaker is Washington State Historic Preservation Officer Allyson Brooks.
  • The Present: This portion includes speakers from the Alliance for Pioneer Square and sports teams, as well as residents.

The next exhibit, Moving Land, shows visitors how natural and cultural forces have transformed Seattle's landscape over time. Along one wall, the exhibit tells the story of nature's engineering of the landscape through glaciers, lahars (moving fluid masses of volcanic debris and water), earthquakes, and tsunamis. A multimedia component provides a history of the geological landscape of Puget Sound over the past 20,000 years, and a "wheel of time," a painting created by local artist Donald Fels, shows the evolution of Seattle's landscape from glaciers to the present day. The wheel rotates, and a viewing window gives a snapshot of what Seattle looked like during those points in time.

With geotechnical and archaeological soil cores at their backs, visitors to Milepost 31 are watching a video animation that shows the last 150 years of human history in Pioneer Square, including the dramatic reshaping of the landscape by grading and filling on a massive scale.

On another wall, the exhibit highlights the impacts of human engineering on the region, including filling in tidelands and regrading for building infrastructure. A multimedia component explains landscape changes through maps and bird's-eye views from the last 150 years.

Puyallup Tribe member Shaun Peterson carved this canoe paddle for Milepost 31. He combined modern techniques with traditional materials to place the iconic image of Chief Seattle on the paddle, underscoring the continued significance of Pioneer Square to native peoples today.

A freestanding exhibit of four soil cores from the Pioneer Square area conceptually ties together the Moving Land exhibit. The various soil layers are identified and keyed to the exhibits on the walls. The soil cores represent a visible reminder of the deep history that literally lies beneath visitors' feet.

Visitors listen to a project engineer. The information center includes visualizations and models of the future tunnel portals to the north and south of downtown Seattle, as well as animations and models that illustrate the tunneling process.

The Moving People exhibit tracks transportation over time using text and photographs to show how people-moving has evolved in and around Seattle. The focus is on making connections between the past, present, and future and the continuation of transportation modes such as boats and interurban rail. A segment on land transportation focuses on trails, rails, and roads. Displays on water transportation highlight canoe culture, ports and piers, and ferries. This section tells the story of the mosquito fleet, small ferries that plied the waters of Puget Sound in the early 20th century. A commissioned canoe paddle carved by Puyallup Tribe member Shaun Peterson, along with archaeological artifacts recovered as part of the project's environmental compliance process, round out the Moving People exhibit.

The final exhibit, Moving Forward, focuses on the new tunnel and the future of Pioneer Square, highlighting the construction project and its extreme engineering. The primary focus is the science of bored tunneling, and the intention is to have visitors walk away with an understanding of this historic project -- and a sense of amazement.

The exhibit also provides information on the history of tunneling in Seattle and WSDOT's tunnel-boring machine. The display puts the tunnel into context alongside related projects to rebuild the city's seawall and create 26 city blocks of new public open space on Seattle's waterfront, showing the future of Pioneer Square once it is reconnected to Elliott Bay. Other elements include a three-dimensional model of the tunnel-boring machine and a hands-on display of cutting wheels from the machine. A looping video provides clips of children sharing their visions of the future of transportation.

The final component of the information center is a display of brochures and announcements about the various construction projects planned, underway, and completed in the neighborhood. A television monitor on a swing arm, visible through the storefront window, provides information even when the center is closed.

Awards Received by Milepost 31

In addition to visitation numbers, WSDOT counts as evidence of the center's success the following recognition from peers at other agencies and within the preservation and museum communities:

  • King County Executive's John D. Spellman Award for Exemplary Achievement in Historic Preservation
  • Washington Museum Association's Award of Project Excellence
  • American Association for State and Local History's Award of Merit and History in Progress Award
  • FHWA's Exemplary Human Environment Initiatives, Education and Training Programs Award

In supporting the nomination of Milepost 31 for these awards, State Historic Preservation Officer Allyson Brooks wrote, "Milepost 31 is an excellent example of historical research and exhibition being conducted in the public interest."

Milepost 31 as a Milestone

During its first year, Milepost 31 welcomed nearly 7,500 visitors from the local community, other parts of the United States, and even from around the world. WSDOT and its partners hope that people who visit Milepost 31 also will visit businesses while they are in the neighborhood.

WSDOT is reaching out to target audiences who live and work in Pioneer Square, residents of other city neighborhoods, and local tourism offices such as Seattle's Convention and Visitors Bureau to increase visitation. The department has committed to keeping the center open 2 years and will use Milepost 31's attendance numbers to gauge its success in drawing people into the neighborhood. The content and displays are all property of WSDOT and may be repurposed for future use on other projects as well. Demographic data gathered from visitor logs, visitor surveys, and comment cards will be used to determine whether WSDOT's marketing efforts, such as radio and print advertisements as well as brochures, are reaching intended audiences. The surveys also could solicit suggestions on ways to keep the center's content fresh and vibrant.

Community advocates have offered additional reviews of Milepost 31. Leslie Smith, executive director of the Alliance for Pioneer Square, says that thanks to the center's "creative and engaging exhibits about Pioneer Square's past, Milepost 31 is quickly becoming a cultural asset within Seattle's most historic neighborhood."

Community developer and preservationist Kevin Daniels echoes this sentiment. "Pioneer Square is a neighborhood in transition," he says. "Neighbors have made great strides to improve Pioneer Square in recent years, and those of us charged with sustaining that effort and protecting the neighborhood's history feel that Milepost 31 is the best way to honor Pioneer Square's history and illustrate all the good things the neighborhood has to look forward to when WSDOT completes the Alaskan Way Viaduct Replacement Project."

In opening Milepost 31, FHWA and WSDOT have created a new model for fulfilling an agency's Section 106 commitments. The success of Milepost 31 demonstrates how consultation and collaboration can lead to creative solutions to mitigate the impacts of transportation projects and, in this case, help ensure the continued economic vitality of one of the Nation's oldest historic districts.

At Milepost 31, these young visitors and Washington State Secretary of Transportation Paula Hammond are examining a model of the world's largest tunnelboring machine.


Kevin M. Bartoy is a cultural resources specialist with WSDOT. He has a bachelor's degree in history from the University of Oregon and a master's in anthropology with a specialization in historical archaeology from the College of William and Mary. He is a Ph.D. candidate in anthropology at the University of California, Berkeley.

For more information, visit, or contact Kevin M. Bartoy at 206–491–9242 or