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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
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.
Highway without an auxiliary lane
Highway with 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.
Auxiliary lanes provide drivers with more space to merge safely.
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
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
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.