What is an auxiliary lane?

Proposed auxiliary lane additions are highlighted in rendering of highway.

Visualization of proposed auxiliary lanes (highlighted in orange)

An auxiliary lane connects an on-ramp directly to the next off-ramp on a highway. With an auxiliary lane, vehicles will not need to merge into the two through lanes of I-5 before exiting. This will reduce rear-end and sideswipe crashes, which are both major causes of delay.

As an example, nearly 99 percent of vehicles that get on I-5 heading south from the Fremont Bridge (I-405) exit at either Broadway, I-84, or Morrison Bridge – all exits within the project area. With the auxiliary lane, these vehicles connecting from I-405 to the exits within the project area no longer have to merge in and out of traffic in the two through lanes.

Adding auxiliary lanes and shoulders is expected to reduce crashes up to 50 percent on I-5 and save drivers 2.5 million hours of delay each year.