Traffic improvements across all lanes for most trips 

Today, I-405 experiences traffic congestion many hours of the day in all lanes. Without the project, we expect these traffic conditions to worse and speeds to decrease. Overall, the I-405 Renton to Bellevue Widening and Express Toll Lanes construction contract is expected to reduce congestion across all lanes in most areas. Because this project adds a new lane in each direction, all travel lanes on I-405 would operate with faster, more reliable trips and would accommodate more vehicles than without the project.

With the project, average travel times during the morning and afternoon peak periods would improve in both the general purpose and express toll lanes. The greatest improvement would be for northbound travelers during the morning commute between I-5 and I-90. For this trip in 2025, travelers would save about 18 minutes in the general purpose lanes and about five minutes in the express toll lanes compared to conditions without the project. However, carpools with two people who choose not to pay a toll, would see increased travel times by one to five minutes in 2045 because they would be traveling in the general purpose lanes, and not in the HOV lane as they do today.

Traffic congestion would also improve on southbound I-405 between Renton and Bellevue during the afternoon commute. However, the EA explains that because more vehicles would be able to access southbound SR 167, congestion would increase near the S. 277th Street interchange. WSDOT has identified that building a new auxiliary lane between SR 516 and S. 277th Street would address this bottleneck, however this separate improvement is currently unfunded.

Transit riders and carpoolers would benefit from the project. The addition of express toll lanes, as well as direct access ramps and inline transit stations, would increase travel speeds and improve reliability for transit on I-405. The project is essential to provide speed for Sound Transit’s new I-405 Bus Rapid Transit line from Lynnwood to Burien, scheduled to open in 2024.

Tolling and socioeconomic considerations 

The addition of express toll lanes would improve I-405 speed and reliability for drivers who choose to use them. These benefits are especially important for carpools and transit, including riders of Sound Transit’s new I-405 Bus Rapid Transit line from Lynnwood to Tukwila, scheduled to open in 2024.

When combined with existing and future improvements, this project would create a continuous 40-mile express toll lane system on I-405 and SR 167 between I-5 in Lynnwood and the Pierce County Line. Express toll lane rules for this segment would need to be set by the Washington State Transportation Commission but are assumed to be similar to the Bellevue to Lynnwood operations.

WSDOT and FHWA examined the effects of the cost of the tolls and all-electronic toll system on low income and minority persons, and persons with limited English proficiency, known collectively as environmental justice populations. Any toll that charges all users the same amount, regardless of income, disproportionately affects low-income users. These effects would be offset by improved travel times and reliability in most locations in both the general purpose lanes and the express toll lanes. The project would not change the number of general purpose lanes or reduce general purpose capacity.

Environmental enhancements

• Stormwater and water quality: The project would treat stormwater to address the new expanded highway area, plus about half of the existing roadway area that is currently not being treated. The Project would reduce the quantities of most pollutants in stormwater compared to existing conditions.
• Ecosystems: The project is being designed to limit effects on local ecosystems as much as possible. The project would permanently affect about 5.3 acres of wetlands and result in temporary loss of less than one acre of wetlands. All wetland impacts will be fully mitigated. WSDOT will construct new culverts and a structure for fish passage on three streams. Across the 11.9-mile project, a total of 77 acres of roadside vegetation would be affected. This vegetation is mostly of low habitat value (weedy or landscaped areas). WSDOT will replant 48 acres of vegetation to mitigate for temporary impacts during construction.

Community effects

• Air quality: WSDOT’s analysis shows that with improved vehicle technology and reduced idling, we expect improvements in overall air quality and reductions in greenhouse gas emissions as compared to existing conditions. Project construction would temporarily affect air quality because of increased equipment emissions and activities.
• Noise: As part of the project, WSDOT plans to build four new noise walls and would relocate two existing noise walls.
• Effects on adjacent properties: WSDOT would affect a total of 54 properties totaling 5.6 acres of property. Specifically, WSDOT would fully acquire five properties – three residential and two commercial. In addition, 49 other properties would be affected by partial acquisitions, permanent easements, or temporary construction easements. WSDOT expects the effects of these acquisitions to be minor compared with the large amount of land in the area and the transportation and mobility benefits provided by the project.
• Local connections and trails: The Project would improve connections for bicyclists and pedestrians by building a portion of the Eastside Rail Corridor Regional Trail in partnership with King County.
• Visual quality: For pedestrians and cyclists on the Lake Washington Trail, the Project would have a beneficial impact on visual quality by relocating the trail to the Eastside Rail Corridor, thus limiting exposure to and awareness of highway traffic, lights, and glare on I-405. At several interchange areas, the project would adversely impact visual quality by clearing vegetation and adding more urban elements, such as lights, signage, retaining walls, ramps and bus stations.
• Other resources analyzed: The Project would have few effects on geology and soils; hazardous materials; energy and greenhouse gases; historic, cultural, and archaeological resources; parks and recreation lands; and public services and utilities.

View and download the full Environmental Assessment and Discipline Reports