The Highway 2 trestle bridge connects Highway 2 to I-5 just north of Everett, crossing over the Snohomish River and wetlands below. The eastbound trestle was built in the 1990s, has three lanes of traffic, and has no immediate need for replacement. The westbound trestle was built in 1968, carries only two lanes of traffic, and over the long term requires replacement. As it reaches the end of its planned lifecycle, there will be an increasing need for maintenance. The existing bridge has no provision for people walking or rolling. There have been complaints of traffic congestion, as the area around Lake Stevens has had significant growth.
And the bridge may not need replacement yet, according to this WSDOT study from 2018:
In 2011, the Washington State Department of Transportation (WSDOT) completed a phased rehabilitation project of the westbound trestle applying carbon fiber wrap to the girders. At the time of construction, this project was expected to extend the service life of the westbound trestle until approximately 2045. (US 2 Westbound Trestle Funding and Finance Study, p. 1)
This follow-up report from 2021 concludes that widening the bridge would not decrease traffic congestion, and in fact would slow down traffic:
Increasing the capacity of the US 2 westbound trestle does not alleviate congestion during the morning peak hours. The analysis found that the increased demand generated by a larger trestle could not be accommodated by I-5 and resulted in longer travel times across the westbound trestle. US 2 Westbound Trestle PEL study p. ES-1
93% of the passenger vehicles that currently travel over the bridge are single occupancy.
The report notes environmental concerns which would have to be addressed, including "climate vulnerability, historic bridges, environmental justice populations, habitat connectivity, wetlands, fish passage barriers, and the presence of protected species and habitat".
WSDOT is proposing replacing the current bridge, which has two traffic lanes with a new bridge that has three lanes for cars (two general purpose and one HOV/transit lane) and a bike/ped lane. They also have a proposal for a two or a four lane replacement.
The trestle bridge is approximately 2.5 miles long (see pg 1-5). All configurations studied by WSDOT had a single-lane ramp connection from the west end of the bridge to I-5 north. Connections to I-5 south included either single or double lane general traffic, with a possibility of an additional HOV bypass ramp. There are also connections to downtown Everett.
WSDOT has some initial cost estimates from 2017 for replacing the bridge. A three lane replacement would cost around $888M, or somewhere between $620M and $1.3B. A four lane replacement would cost between $700M and $1.5B.
Highway pavement lasts 12-15 years. New bridges are designed for a 75 year lifespan.
Rule of thumb for required maintenance cost for bridges is 1-3% of the total cost of replacing the bridge per year. (from the Seattle Bridge Audit p. 10).
Traffic levels on the Highway 2 trestle bridge are currently around 18,000 vehicles per day in both directions. Only half of the bridge is bring replaced, so we'll assume there are about 9,000 trips per day on the westbound portion. That's 3,285,000 per year. Let's say the new bridge cost $1B, but spread out over a 75 year lifespan, the cost is 13,333,333 for each year the bridge is in operation. That's a cost per vehicle per trip of $4, and this isn't including any fees required for financing.
WSDOT has done engagement with the public on a new bridge. Here are their results:
Top three problems with the existing trestle
More than 58% believe the problem is not enough lanes.
53% said population growth has overwhelmed the trestle.
45% said the existing ramp to southbound I-5 can't accommodate peak period traffic.
Use of transit, carpooling/vanpooling
More than 55% said they will not use transit.
29% said direct transit service with no or fewer transfers would encourage them to use it or use it more often.
26% said a dedicated HOV lane would encourage them to try carpooling or vanpooling.
Paying for a new bridge or improvements
41% supported using the existing gas tax.
28% did not support using the existing gas tax, user tolls, a Snohomish County tax or a combination.
21% chose "other" and added comments stating opposition to tolls or any additional taxes.