I-205 Corridor Study
Draft Recommended Alternative

July 2001

After considering several improvement packages, and numerous rounds of traffic operations analyses, a recommended alternative has been drafted to address 20-year transportation needs in the I-205 Corridor. An Access Steering Committee has met regularly over the past 9 months to guide development of the Recommended Alternative and the required draft Access Point Decision Report. Input from the Citizens’ Advisory Committee has also guided development of the Recommended Alternative. The basis for the Alternative is the split diamond interchange concept between 18th and 28th Streets (diagram below). The draft set of solutions to address 20-year transportation needs in the I-205 Corridor has emerged after considering safety problems associated with large volumes of merging and weaving traffic. The improvement package includes a system of braided ramps, auxiliary lanes and collector-distributor system components. The recommended I-205 alternative has been developed to not preclude potential High Capacity Transit (HCT) improvements.

Key elements of the alternative include:

• Construct direct connection to NE 112th Avenue from the existing I-205 northbound to Mill Plain west-bound off-ramp. The Mill Plain to I-205 northbound on-ramp is proposed to go over the new connection. This 112th Avenue Connection will be advanced by the City of Vancouver.

The following elements are recommended to provide for significant traffic volumes using I-205 between the Columbia River and Mill Plain, moving between SR-14, I-205 and Mill Plain, and to minimize traffic merging/weaving problems:

• Reconstruct ramps between SR-14 and Mill Plain to braid northbound 2-lane off-ramp from I-205 to Mill Plain over the on-ramp from SR-14 to northbound I-205.
• Reconstruct off-ramps (both eastbound and westbound) from SR-14 connecting to I-205 northbound, to Mill Plain off-ramp and to the 112th Avenue Connection.
• Reconstruct Mill Plain to I-205 southbound on-ramps, braiding the ramps to separate traffic movement from I-205 southbound to SR-14. I-205 southbound to SR-14 traffic will have to exit I-205 in the vicinity of NE 18th Street.

The following elements provide access to and from I-205 for 18th Street traffic and are essentially components of the south half of a new split-diamond interchange:

• Construct 2-lane northbound off-ramp from I-205 to 18th Street (ramp begins in vicinity of Mill Plain).
• Construct northbound frontage road between 18th Street and Burton Road.
• Construct 2-lane southbound on-ramp from 18th Street to I-205.
• Construct southbound frontage road between Burton Road and 18th Street.
• Reconstruct 2-lane southbound off-ramp from I-205 to Mill Plain and “braid” it under the 18th Street on-ramp.

The following elements are recommended to provide for traffic moving between I-205 and SR-500 and to minimize traffic merging/weaving problems:

• Reconstruct 2-lane northbound off-ramp from I-205 to SR-500.
• Construct flyover from westbound SR-500 to southbound I-205.
• Reconstruct eastbound SR-500 ramp to southbound I-205.

The following elements provide access to and from I-205 for Burton Road/NE 28th Street traffic and are essentially components of the north half of a new split-diamond interchange:

• Construct southbound off ramp from I-205 to Burton Road.
• Construct northbound on-ramp from Burton Road to I-205, braided to separate the traffic from the northbound SR-500 off-ramp traffic.

The following elements provide for the growing traffic on mainline I-205 between SR-500 and Padden Parkway (NE 83rd Street) interchange:

• Construct auxiliary lanes northbound and southbound on I-205 between SR-500 and Padden Parkway.

It is recognized that the full I-205 Corridor Strategy will require significant financial resources. Therefore, the improvements will need to be staged over time. However, all stages must be able to “stand-alone” and at each stage must meet the FHWA test that the proposed access point does not have a significant adverse impact on the safety and operation of the Interstate facility based on an analysis of current and future traffic.