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Bridge and Highway Lanes

Highway lanes will be added in the five-mile CRC project area to better connect interchanges, improve safety and reduce congestion. The number of lanes will transition to the existing number of lanes at the northern and southern project boundaries.

The replacement I-5 bridge is being designed to accommodate a total of 10 lanes of traffic and full safety shoulders. In each travel direction there will be three through lanes and two lanes to connect interchanges.

Auxiliary lanes safely connect interchanges

An auxiliary, or add/drop, lane connects two or more highway interchanges. These lanes improve safety and reduce congestion by providing space for cars and trucks to reach highway speeds before merging and to slow down before exiting. An “exit only” sign on the highway is an indicator of an auxiliary lane.

With seven closely-spaced interchanges, most highway entrances in the project area require vehicles to merge quickly upon entering the highway. These conditions lead to crashes. An average of 400 crashes a year occur along I-5 in the five-mile project area, a collision rate two times higher than similar highways in Oregon. The Hayden Island interchange on-ramp to northbound I-5 has the highest crash rate on I-5 in Oregon.

Determining the right number of replacement bridge lanes

Local project partners followed regional policies when determining that I-5 should have three through-travel (or general purpose) lanes in each direction through the CRC project area. They also agreed additional lanes should connect some interchanges to allow for safe merging or exiting the highway.

The CRC Project Sponsors Council (PSC) recommended in March 2009 that the replacement bridge should include up to three add/drop lanes in each direction. When combined with the three through lanes in each direction, this would allow the bridge to have up to 12 lanes. The recommendation was based on technical information related to crash rates and public comment. Information on the number of lanes analysis and recommendation can be found here.

In August 2010, the PSC members unanimously agreed on a set of recommendations to the Governors of Washington and Oregon to move ahead with development and construction of the I-5 bridge project. The recommendations include designing a replacement bridge with three through lanes, two auxiliary lanes and full safety shoulders in each direction, making a 10-lane bridge facility. These recommendations came as result of work completed by an integrated group of staff members from all agencies represented on the council, as well as the ports of Portland and Vancouver. The analysis found a 10-lane bridge performs similarly to a 12-lane crossing.

Better operations and reduced congestion

Auxiliary lanes improve highway function through more efficient merging, both on and off of the highway. Auxiliary lanes can serve local connections between Marine Drive, Hayden Island and Vancouver; provide better connections for freight from I-5 to the ports; and result in less spillover traffic to city streets.

Congestion within the project area will be reduced by 70 percent compared to No Build conditions with all planned project improvements, including building auxiliary lanes.