As angry drivers stew about another nightmare drive from West Seattle, the city admits it didn’t know it could ask the Coast Guard to delay a bridge opening that blocked the only alternate route.

For the second time this month, the Coast Guard raised the Lower Spokane Street Bridge Wednesday morning while drivers were trying to maneuver around a crash that snarled the West Seattle Bridge.

Coast Guard Chief Petty Officer Sara Mooers says the Seattle Department of Transportation could have asked for a delay in the bridge opening Wednesday or last week, but never did.

When I asked the city why it didn’t ask, Rick Sheridan, Seattle Department of Transportation spokesperson, told me the city wasn’t aware that it could make such a request. The city only thought it could ask for a postponement if there was a problem with the bridge itself.

While the 520 bridge remains closed to boat traffic during commute times, the Coast Guard explained that the Lower Spokane Street Bridge operates under different rules.

The Duwamish handles a huge amount of commercial maritime traffic that is dependent on the tides. When large boats need to move, they need to move, regardless of bad traffic on the West Seattle Bridge.

Steven Fischer, the Coast Guard’s bridge administrator for the Seattle District, said it’s difficult to postpone an opening once a large vessel starts moving.

“This isn’t a car or a commercial truck,” he said. “You don’t stop on the bridge, put your emergency brake on, take a nap, and wait for somebody to honk their horn for you to go. It’s a very dangerous and dynamic thing to hold up a tug and barge in a narrow waterway like that.”

The Coast Guard said the city of Seattle knew there could be conflicts when it chose to put a low bridge on the Duwamish River, which the Coast Guard considers an obstruction.

“The Coast Guard, at the time, warned the city ‘here’s the impact and here’s what you’re going to have to do if you build a low bridge,’ and they chose to (build it anyway). So we’re kind of hamstrung by choices made previously,” said John Moriarty, Coast Guard deputy for waterways management.

In 2008, the city of Seattle asked if the Coast Guard would consider changing its rules to prevent rush hour openings. After a long public comment process and study, it was denied because the commercial importance of traffic on the Duwamish River outweighed the other concerns.