The page you requested has moved and you've automatically been taken to its new location.

Please update your link or bookmark after closing this notice.

Skip to content U.S. Department of Transportation/Federal Highway AdministrationU.S. Department of Transportation/Federal Highway Administration
Office of Planning, Environment, & Realty (HEP)

Washington State DOT I-405 Corridor Plan

Name of Tool: "Tier 1" EIS and Transportation Corridor Plan

Implementing Agency: Washington State DOT

Scale of Application: State/regional planning, corridor/subarea planning

Description: From 1999-2002, WSDOT and numerous partners developed a master plan for the heavily-congested corridor along Interstate 405 in east suburban Seattle. The corridor team also produced a Tier 1 Environmental Impact Statement (EIS), a streamlined planning tool that addresses large-scale issues, providing guidance and background for incorporation into the environmental assessments of the Corridor Plan's 300 proposed component projects. "Smart growth" land use strategies account for approximately $95 million of the nearly $11 billion in estimated cost for the 300 projects identified by the preferred alternative in the Corridor Plan and EIS.

Purpose and Need

Interstate 405 in east suburban Seattle accommodates over 900,000 people daily, making it Washington state's second most heavily traveled expressway. The 30 mile corridor, which runs north-south and parallels Seattle's Interstate 5, originally served as a bypass route. Today, however, high growth rates in population, employment, and traffic congestion characterize the largely suburban region that surrounds the corridor. Sharing a mutual concern for improving mobility in the corridor, Washington State DOT (WSDOT), the state legislature, residents, businesses, and local leaders cooperated in the development of environmental documentation and a Corridor Plan to address transportation needs in the I-405 Corridor.

The resulting Corridor Plan envisions a multi-modal program of improvements, including land use strategies and community amenities as well as expansion of general purpose freeway capacity, high occupancy vehicle (HOV) lanes, vanpools, and transit, as the most appropriate and effective approach to addressing mobility problems. Underlying the plan is a strategy of investment in transportation facility expansion and improvement within the Seattle region's designated urban growth area, rather than outside of this area. As a product of the planning process, a Tier 1 corridor EIS also was completed that aims to streamline environmental assessments of individual component projects as they come on line, thereby facilitating implementation of the overall plan.


In 1999, WSDOT initiated the I-405 Corridor Program. Backed by strong financial support from the state legislature and a desire among local communities, leaders, and interest groups to address regional mobility concerns, the program completed both a corridor-wide EIS and a long-term master plan. In the EIS, WSDOT considered several transportation alternatives including a transit- and management-focused alternative, a general capacity (freeway expansion) alternative, and two "mixed mode" alternatives combining infrastructure expansion with management strategies and transit. The Corridor Plan focuses on the recommended "mixed mode" alternative and describes its components, a timeline, and funding needs over the next 20-30 years.

Ultimately, according to the plan, the I-405 corridor will feature two new expressway lanes in each direction, about 15 access and exit points for HOV lanes, ten bus rapid transit stations, 5,000 new park-and-ride parking spots spread over about 20 facilities, nine transit centers, expanded transit and vanpool service, development of activity centers through land use changes, and a comprehensive transportation demand management program. More importantly, all of these investments are focused within the designated growth area surrounding east Seattle. According to Michael Cummings, project manager for the I-405 Corridor Plan, the plan offers the region's leaders and residents an outline for future transportation strategies. "In essence," says Cummings, "[they] have something to coalesce around." Since the implementation will occur in stages, piece by piece rather than all at once, the role of the plan is to guide that investment strategy over time.

One of the program's early steps was designation of a corridor executive committee, consisting of municipal and county officials, regional representatives, state legislators, and representatives of state and federal agencies. Among the committee's responsibilities, as listed in the group charter, are "to provide vision, policy, and oversight in the development of the I-405 Corridor Program; to provide funding strategy and advocacy; to assure regional balance; and to achieve consensus on I-405 investments." Through monthly meetings, open to the public, the committee ensures that public involvement remains a critical input into the decision-making process. According to Cummings, participants in the plan's development "reached agreement at every step" in the process. Cummings largely credits the committee for holding together the coalition of stakeholders within the corridor throughout the development of the plan and now during the beginning of its implementation. The committee, having stayed together throughout the process of developing the plan, now acts as a sort of "kick-off point" for component projects within local jurisdictions.

Implementation of the various components of the Corridor Plan faces considerable financial constraints. Washington voters rejected Referendum 51, a statewide gas tax increase that promised nearly $2 billion for I-405, in November 2002. Instead, the state legislature levied a less ambitious five-cent gas tax and committed $485 million to I-405. The legislature also authorized formation of the Regional Transportation Improvement District (RTID), a commission which will raise funds through taxes and fees within the three-county Seattle area and apply funds to projects within the district's boundaries. I-405 supporters anticipate much of the funding for the remainder of the projects will come from the RTID as well as other local, state, and federal sources. Leaders recognize the near impossibility of receiving the estimated $11 billion needed for the plan. Innovative alternatives such as regionally-based congestion tolling, considered as part of the EIS, will complement traditional sources of transportation financing.

Cummings affirms that despite its ambitions, WSDOT recognizes the reality of the financial situation and the nature of long-term planning. As with a long-range transportation plan, corridor stakeholders realized that the conditions and priorities within the corridor would evolve over time. For example, a destructive earthquake struck the region in February 2001, altering priorities in light of repair needs for damaged highways and bridges, such as the Alaskan Way Viaduct and the State Route 520 bridge over Lake Washington. Rather than viewing the plan as an immediate and flawless solution to the mobility problems, implementing agencies and member jurisdictions pragmatically view it instead as a strategy for long-term, future investment. As funds for the corridor become available, leaders will apply them according to the goals and priorities as described by the plan.

The purpose of the corridor-wide Tier 1 EIS, a second product of the Corridor Program, is to address environmental issues of broad concern throughout the corridor. Cummings describes the EIS as a document that addresses "cumulative impacts" of transportation infrastructure expansion over time. As with the funding, which will be allocated incrementally to implement pieces of the plan, environmental assessments (EAs) will be carried out over time on each individual project. Using the Tier 1 EIS as a guide to identify issues that have already been discussed and debated by the community, the assessments can be carried out much more quickly, saving money and advancing the objectives of the plan more swiftly.

Application Examples

Several projects outlined in the corridor plan are underway as of 2004, including three "Nickel Projects"-those funded by the five-cent gas tax-to expand highway capacity. In addition, the city of Kirkland is following up on its plans to develop transit and mixed-use activity centers, tasks that are indicative of similar work in other cities.

The first funded components of the Corridor Plan are three distinct segments of general purpose lane additions to I-405. Known as the "Nickel Projects," in 2004 these three improvements are entering the EA phase, which involves community meetings to identify areas of particular concern. Each EA will rely on the Tier 1 EIS for background. Specifically, according to I-405 Project Manager Craig Stone, "the Tier 1 has allowed us to focus on the specific impacts without having to consider cumulative impacts" for component projects. Since the Tier 1 EIS considered alternatives for the entire program of improvements for I-405, the component projects' EAs focus on more project-specific issues such as culvert crossings, final roadway alignments, sound wall design, and traffic control plans for construction.

According to Stone, the comprehensive nature of the Corridor Plan allows for time savings and more sensible timing and design of projects. For example, Sound Transit is building a direct access overhead ramp to the Interstate to serve express buses. Because the project team can anticipate future expansion of the Interstate, as called for in the Corridor Plan, the design of the bus ramp will accommodate the future geometric needs of the expanded travel lanes beneath.

Although initiating work before the start of the corridor program, the City of Kirkland has produced and begun to implement a land use plan for Totem Lake, emphasizing the creation of transit villages, mixed-use communities, and high density development. In June 2004, the city published a request for proposals to redevelop a property in downtown Kirkland into a mixed-use building and transit center. The development is consistent with both the Corridor Plan and EIS, which identified downtown Kirkland as a priority location for a transit center.

While it is difficult to attribute new or anticipated land development along I-405 to the Corridor Plan, project participants emphasize that concentration of new transportation facilities, infrastructure improvements, and expanded transit service is within the urban growth area for the Seattle region, as designated under state law. As the populations of towns such as Kirkland and others continue to grow, facilitated in part by the concentration of transportation improvements within the growth boundary, towns will have little choice but to increase densities. The Corridor Plan recognizes this necessity and, as a result, emphasizes the value to communities of encouraging transit villages, mixed-use developments, and higher density developments.

Successes and Lessons Learned

According to Cummings, the key to the success of the development of the Corridor Plan was communication among stakeholders, facilitated by the corridor executive committee. Strong support from the legislature further helped to solidify support among the constituencies within the corridor.

Another imperative to the success of a project like I-405 is maintaining a long-term vision, even in the face of short term funding hurdles. Cummings recognizes the fiscal reality in Washington: "Costs become large, sometimes unimaginably so. People start to think and say [about the Corridor Plan], "It's too expensive. We can't afford it. We can't do it." Nevertheless, he maintains that long-term planning is a necessity because "if you do not do it, you end up taking care of smaller scale projects, here and there, moving problems from one location to another," essentially rearranging deck chairs on the Titanic.

Perhaps the most valuable outcome of the corridor planning process is that people now understand that the corridor is a large, interdependent community with shared problems and shared needs. Because funding and resources are constrained, as funding becomes available, certain jurisdictions may be disappointed that the plan's components addressing their local needs do not receive immediate attention. But most of them recognize that other things are more important. Says Cummings, "Our strategy is "worst first'. And people understand that throughout the corridor, because most people use the entire corridor." Even in some "worst first" cases, WSDOT and other implementing agencies may not have the resources to fully address the worst problem, so they apply those available funds elsewhere; as a result of the plan, most stakeholders also understand and appreciate that strategy.

This notion of sacrifice, or at least patience, also grew out of the crafting of the plan as a large-scale, forward-looking document. For example, the City of Kirkland's representatives to the I-405 program were, according to Planning Director Eric Shields, more inclined toward a transit-based solution and less enthusiastic about the selected alternative than other participants. Despite this, even Shields recognizes that, outside of his local jurisdiction, other needs must be addressed with limited resources. This demonstrates that, even where the particular elements selected for the plan could not satisfy all stakeholders, the program did achieve a strong level of cooperation and understanding within the corridor which should pay dividends throughout the implementation phases.

For Further Information


Michael Cummings
I-405 Corridor Plan Project Manager
Washington State DOT

Web Sites and Publications:

Updated: 10/20/2015
HEP Home Planning Environment Real Estate
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000