Bridges and Roadway Structures
Other Roadway Structures
For more information about Seattle Bridges and Roadway Structures, call 206-386-4251.
Areas of Seattle are notoriously hilly, and with the region's heavy rains, landslides are a common occurence in many neighborhoods. This has created the need for retaining walls to keep smaller slopes intact, to protect public streets and other public areas.
SDOT maintains close to 600 retaining walls in Seattle, most protecting public streets. The average height is six feet, and if all the retaining walls and seawalls were lined up end to end, they would extend for 21 miles.
Retaining Wall Maintenance Program
The Roadway Structures Division of SDOT conducts an ongoing program to inspect and maintain retaining walls which deteriorate over time or that are damaged by floods, landslides, earthquakes, or other causes. Approximately $400,000 per year is allocated for this program, which enables the department to make major repairs from one to six walls, depending on the size of the individual projects.
Alaskan Way, downtown Seattle's western-most arterial that runs along the shores of Elliott Bay, serves as a vital economic, transportation and social link for the City of Seattle. Most people do not realize it, but when they drive on Alaskan Way between Bay and Washington streets, they are driving above a timber bridge!
Alaskan Way has several sections of seawalls that form a buffer against the waters of Elliott Bay. The Alaskan Way Seawall was originally completed in 1934 in an effort to extend the city's waterfront, ease north/south automobile and railroad travel and make it easier to load and unload cargo from the many ships that sail into the Port of Seattle.
In order to extend the waterfront and support traffic, city engineers built Alaskan Way and the Alaskan Way Seawall out of wooden platforms, steel sheet piling, concrete and dirt from the Cedar River. Hundreds of steel panels were linked side by side over 50 feet from shore to form a barrier against the waters of the Puget Sound. Between the seawall panels and the shore, thousands of wooden pilings were driven into the mud to form a support for a platform for Alaskan Way. Once the pilings were installed, soil was then placed to fill to the top of the pilings and a timber platform was laid that interlocked with both the supporting pilings and the steel seawall. A layer of dirt, 12 feet deep, was placed on top of the platform, and then Alaskan Way was paved and bordered with a concrete sidewalk barrier.
Today, SDOT maintains the Alaskan Way Seawall and several other seawalls with an inspection program and routine repairs.
Stairways and Stairway Maintenance Program
SDOT owns over 480 stairways, totaling over six miles, that are used by pedestrians to "short cut" their way up or down a hill, to get from one street to another, or to serve a public area such as schools, parks, playgrounds, senior centers and bus stops.
Stairway Maintenance Program
Due to the steep and sloping nature of Seattle’s landscape, many of Seattle’s streets are connected by pedestrian stairways. The stairway maintenance program was initially developed to rehabilitate "slab and rail" stairways built between 1945 and 1965. They are basically concrete slabs set on top of concrete blocks, with at timber handrail. They were a low cost alternative to the longer lasting and more ornate reinforced cast concrete stairways built during the 1920s and 30s. About 130 of 450 SDOT-owned stairways are of this type.
The SDOT Roadway Structures Division conducts a periodic inspection program to develop a list of stairways for repairs. Repairs range from replacing the handrail to removing and replacing the landings, treads, or concrete slabs. The list is prioritized and the work is scheduled accordingly. The 2006 budget for stairway maintenance is approximately $177,000. This will fund the repair or retrofit of approximately 30 to 50 stairways, depending on the work needed for each stairway. The City has also set an additional $375,000 aside this year for major stairway rehab work.
Battery Street Tunnel
The Battery Street Tunnel is owned by Washington State and maintained by the Seattle Department of Transportation. Built in 1952, the tunnel is 3,140-feet-long and is made up of two separate tunnels, or "bores" that allow traffic to travel south and north bound along Highway 99. The Battery Street Tunnel is equipped with drainage, ventilation and fire suppression systems. SDOT maintains the tunnel on a regular basis.