If you are one of the more than 200,000 drivers that travel along Interstate 10 in Phoenix on an average day, you may have noticed an area covered by a chain link fence between the Eastbound and Westbound lanes of the Deck Park Tunnel. What is that area, and why is it there? That's what I am going to explore in this post.
 |
What is that mysterious, fenced-off area between the eastbound and westbound tunnels?
Photo: North Phoenix Blog
|
A New Transcontinental Highway
With the stroke of a pen, President Dwight D. Eisenhower signed the Federal Aid Highway Act of 1956, authorizing the creation of thousands of miles of Interstate Highways in America. Eisenhower believed that a national network of high-quality roads was essential to national defense, allowing troops and equipment to be moved quickly and efficiently.
The project called for a new transcontinental route that would later become Interstate 10. During the next three decades, Interstate 10 would grow to connect Santa Monica, California to Jacksonville, Florida, spanning nine states and 2,460 miles (3,959 km) from end to end.
A 392-mile segment of the route would traverse across Arizona, beginning at the Colorado River crossing at the California border and continuing westward to Phoenix, veering southeast to Tucson, and then east towards New Mexico.
The Arizona Highway Department laid out the route for Interstate from 1956 to 1958. By 1960, a 31-mile stretch of highway connected California to US Route 60 in Arizona. Drivers had to pass through Wickenburg and then Sun City to get to Phoenix. A bypass route opened in June 1973 took an almost straight shot from the border to the edges of the Phoenix metro area.
 |
Map showing routes from California to Phoenix in 1960 and 1973.
By: North Phoenix Blog
|
With Interstate 10 now connecting the California border to the edge of
Phoenix, the next step was figuring out a way to carve a new freeway
route through central Phoenix.
An Unpopular Proposal
Trying to build a new Interstate Highway through the center of an existing city was an extremely difficult task. The first plan was proposed in the 1960s, and it was a wild one. In this design, the freeway would be elevated above ground with wide, arcing “helicoil” ramps designed to minimize disruption of city streets and the utility grid.
The idea was to keep traffic off of downtown city streets by elevating it twenty five feet above ground level. For fourteen blocks in Central Phoenix, between Seventh Avenue and Seventh Street, the span would arch more than a hundred feet above surface streets and sidewalks. The ribbon of concrete would soar ten stories above Central Avenue, with two access/egress helicoils made of spiraling ramps, similar to those in Los Angeles.
Below are two screenshots of the 1966 elevated freeway proposal, taken from the Arizona Department of Transportation Blog
Not surprisingly, this design was rejected by voters in 1973, sending state highway planners back to the drawing board.
A New Plan for Interstate 10
The new plan for Interstate 10 took into account archaeological sites and historic buildings along the route. Most of the route would be built below grade and surrounded by soundproof walls, with six blocks of freeway
running underground through a long tunnel. The surface would be covered with new public parkland.
While it was not the cheapest solution, this plan was praised for its innovative approach to preserving the character of historic and commercial established neighborhoods. This plan was much more appealing to voters, who approved the project in 1979.
 |
Proposal for the Papago Freeway Tunnel from July 1990.
Image: The Final Mile, ADOT, 1990
|
The illustration above includes an Urban Fountain Plaza and a Tree Bosque, which I do not believe were ever built. However, the rest of the plan including the Japanese Friendship Garden, Central Avenue bridge, Performing Arts Center, Open Lawn areas, and the Kenilworth School were retained or built as of this posting in 2021.
The project incorporated many other elements with the local citizens in mind, including soundproof walls, pedestrian bridges, and color and decoration of the concrete walls. Workers removed more than 800 palm trees, maintaining them at a nursery during construction and returning them to the same neighborhoods after construction had been completed.
Construction Begins
Construction of the twenty-mile corridor of Interstate 10 through Central Phoenix began in 1983. Archaeologists discovered the remains of two ancient Hohokam villages on both the east and west sides of Phoenix. One site was called La Ciudad (The City) and included a square mile of canals, ramadas, burial sites, and ball courts. The second site, Los Colinas (The Hills) contained artifacts, pottery, and evidence of early agriculture.
 |
Archaeologists work to excavate La Ciudad, an ancient Hohokam settlement discovered in Phoenix in the 1980s during the construction of the Interstate 10 freeway. Photo by: Jeff Kida.
|
Once the archaeological sites had been excavated and catalogued, construction began on the final stretch of Interstate 10 from the Moreland district to 20th St. This was the last segment of Interstate 10 to be completed along its entire transcontinental route.
Papago Freeway Tunnel
Engineers and designers rose to the challenge by designing a six-block,
2,887-foot section of the freeway below grade with a public park on top.
The below-grade section, officially called the Papago Freeway Tunnel
and more popularly known as the Deck Park Tunnel, is technically not a
tunnel, but rather 19 bridges lined side by side, that support 13 acres
of the 30-acre Margaret T. Hance park atop the bridge decks. The
structural portion of the tunnel cost more than $55 million and the
electrical and mechanical components cost an additional $20 million.
 |
Construction of the Papago Freeway Tunnel in Phoenix in the 1980s.
|
The New Freeway Opens
The 20-mile portion of I-10 through Phoenix cost more than $500 million, with an additional $150 million in right of way costs. Federal aid, administered through the Federal Highway Administration, accounted for 95 percent of the construction costs. The project employed thousands through the 1980s and was the most expensive freeway segment on the Interstate System when it opened in 1990.
The official completion date of Interstate 10 is recognized as August 10, 1990. On that date, a Grand Opening ceremony was held where Arizona Governor Rose Mofford cut the ribbon. The East Papago segment opened to vehicular traffic on August 23, 1990.
Papago Intermodal Transfer Station
A central section of the Papago Freeway Tunnel was intended to serve as an underground bus terminal. This 1989 illustration from the Arizona Republic newspaper explains that "Two bus lanes on the freeway will be served by a terminal. Riders will be able to take an elevator or escalator up to the deck and catch a bus on Central [Avenue]."
 |
An illustration showing the location of the bus terminal in the central corridor between the eastbound and westbound tunnels of Interstate 10 in Phoenix. Source: Arizona Republic, Nov. 11, 1989
|
The Papago Freeway Tunnel opened in 1990 and has been serving drivers for more than 30 years, but the bus terminal was never completed. So why wasn't it ever finished?
According to the Phoenix New Times: "Unfortunately, despite spending more than $9 million to build the bones
of the structure, the city was never able to secure the $20 million-plus
in federal funds it would have taken to complete the project."
The Tunnel's Legacy
The never-built underground bus terminal was voted "Best Abandoned Transit Project" by the Phoenix New Times in 2011. Their article provides some rare photos of the inside of the space between the tunnels.
 |
Photo by: Phoenix New Times, 2011
|
 |
Entering the never-built bus terminal space
Photo by: Phoenix New Times, 2011 |
 |
Ceiling detail
Photo by: Phoenix New Times, 2011 |
 |
Looking down the length of the corridor
Photo by: Phoenix New Times, 2011 |
Now you know the answer as to what is behind those mysterious chain-link
gates! It's an empty space, intended for an underground bus station
that was never completed.
Further Reading
The Arizona Department of Transportation has a blog where they have written extensively about the history of Interstate 10 in Arizona, including the Deck Park Tunnel. Please visit the link below to visit their site, where you can read more about the tunnel's history, facts and figures, see construction photos, and much more.
https://azdot.gov/tags/deck-park-tunnel
