How does SDOT cool down Seattle’s bridges during extreme heat?
Jul 22, 2026, 4:49 PM | Updated: 4:50 pm
A wide view of the Ship Canal Bridge in Seattle. (Photo courtesy of the Seattle Department of Transportation via KIRO 7)
(Photo courtesy of the Seattle Department of Transportation via KIRO 7)
Today is a Pinpoint Alert Day. KIRO 7’s meteorologists called for the alert because it will likely be the hottest day of the year so far.
Extreme heat can cause damage to our roads and bridges.
To prevent issues, crews with the Seattle Department of Transportation (SDOT) periodically spray down the Ballard, Fremont, and University bridges with water.
The cooling process, which prevents metal expansion during extreme heat, requires at least 85-degree Fahrenheit temperatures for three consecutive days with high nighttime temperatures.
KIRO 7 News reached out to SDOT about this week’s heat to find out whether it meets the threshold. The agency said it does not, so crews will not be spraying the bridges today.
Why cool the bridges?
According to SDOT, metal expansion can affect the ability of the city’s steel bridges to open or close properly. This can cause the bridges to get stuck, leading to traffic delays for both cars and boats. This cooling method is the best tool available to keep these historic bridges functioning properly and to avoid major disruptions during heatwaves.
How long does the cooling process take?
The cooling process typically takes about 10 minutes. A tanker truck drives across the bridge and sprays the steel down with water. This is done every hour or 2 hours between noon and 7 p.m., depending on how hot the day is.
Crews treat the water with Vitamin C because it is better for fish. The Vitamin C neutralizes the chlorination found in normal drinking water, which is known to harm fish gills.
How often are Seattle’s bridges cooled off?
Bridge cooling is typically done approximately a dozen times per summer, usually from late July into late August. The operation is a strategy to adapt to rising temperatures in the region rather than a structural repair. So far this year, bridge cooling has not been needed.
