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Vehicle weight restrictions for bridges in unincorporated King County

Ames Lake Trestle Bridge.

Example of a weight restricted bridge. The Ames Lake Trestle Bridge was built nearly 100 years ago and was originally designed with narrow lanes for much smaller vehicles compared with what we see on the road today. The bridge has a posted weight restriction for specific large trucks and specialized hauling vehicles. A project to replace Ames Lake Trestle Bridge is anticipated to begin in spring 2024.

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This page provides the latest updates on bridges with weight restrictions and links to complete lists of bridges with vehicle weight, height, speed and other restrictions. Below are frequently-asked questions, the latest list of load limited bridges, and links to pertinent permit applications and webpages.

List of bridges with vehicle weight restrictions

Frequently asked questions

The Federal Highway Administration (FHWA) developed updated criteria for determining the weight that a bridge can safely carry 10 years ago. All state and local governments evaluated publicly owned vehicle bridges using these criteria and determined whether additional vehicle weight restrictions must be placed on bridges.

Key components:

• Requirement to rate bridge’s ability to carry four additional types of “special haul vehicles.” These are authorized vehicles on roadways that can have heavier loads.

• Requirement to evaluate and rate the gusset plates. A gusset plate is used in between the intersection of two columns or beams and in connection points on bridges with steel trusses.   

All vehicle bridges managed by the county are inspected at minimum of every 2 years. 

The weight restrictions do not affect pedestrians, bicycles, cars, and typical passenger vehicles.  List of restricted bridges (573KB)

No. Speed limits are not based on weight restrictions.

Engineers evaluate critical bridges that may need weight restrictions to determine if additional strengthening could be performed. Three bridges were load upgraded in 2022-2023 and no longer have weight restrictions. The county had an active seismic upgrade program for bridges from 1992 to 2006. Most of the improvements that could be done to strengthen older bridges was done at that time.

Many vehicles like school buses, fire engines and ambulances are still allowed depending on their weight and the loads they carry. We continue to update fire districts if and when there is a weight restriction or a new one is put in place. Truck companies and agencies can email the county at with questions and requests about specific bridges. Inquiries should include information about truck weights, including the weight of any loads, and information on how the vehicle distributes the weight (spacing between each axle and loads on each axle). If the truck, fully loaded, exceed legal loads, or posted load signs, companies or agencies can apply for “over legal load” permits. More about overlegal load permits

Advanced warning signs and turn-around signs are posted on roadways to inform truck drivers that they are approaching a weight restricted bridge.