The city of Seattle has requested that the Coast Guard restrict openings of the Lower Spokane Street swing bridge during rush hours to facilitate traffic coming into and leaving West Seattle.

Councilman Tom Rasmussen, an Alki resident who commutes over the low bridge to work and back most business days, initiated the issue.

"I noticed some long delays and some unnecessary delays during the rush hours," Rasmussen said. "Unless we get help from the Coast Guard, the Port of Seattle, the city and the state, we are in for a very difficult time as the time approaches when the viaduct is closed."

Acting on Rasmussen's request, the Seattle Department of Transportation has written to the Coast Guard's bridge administration commander at the 13th Coast Guard District in Seattle.

The city wants the bridge openings restricted from 7 a.m. to 9 a.m. and from 4 p.m. to 6 p.m. weekdays. The city says it understands "the specialized requirements of vessels or greater than 5,000 tons and would request an exemption from these opening restrictions for those tide-dependent vessels."

The transportation department, "as a standard practice" collects vehicle volume information from permanently embedded sensors at all of its drawbridges, along with logs of the bridge tenders.

The decision to seek restriction of the low bridge openings came after review of the data requested by Rasmussen. Transportation personnel found "compelling reasons" for seeking the restrictions, said an internal report.

"We know surface traffic on the lower bridge is delayed between 5 and 43 minutes per opening event," the report written by city transportation engineer Cynthia Robinson.

She suggested several warning signs that tell of the opening of the swing bridge forces traffic to find detours, which increases congestion on the main West Seattle Bridge.

"There were a total of 598 openings during the study period (last summer), of which 68 were peak period openings and of those there were only 17 vessels passing that carry more than 5,000 tons of cargo," Robinson wrote. "Our request would not impede those tide dependent vessels and would allow them to pass without delay during peak periods."

Robinson's report made it clear that the more openings for more ships, there are more delays for automobile traffic out of and into West Seattle.

"Currently, there is an average of 12 minutes of delay incurred by each vehicle caught on the lower level bridge in each direction," Robinson's report said. "The bridge opens 9 times each month during (the morning) peak, assuming each event is catching approximately 70 eastbound vehicles, over a month there are 630 surface vehicles caught in delay equating to 126 hours of delay every month to (morning) peak eastbound surface traffic due to bridge openings."

She said delays on the lower bridge only adds to the congestion on the high West Seattle Bridge, which the city could ameliorate partly by adding more warning signs along routes to the bridge and to limit maintenance tests of equipment to off-peak times.

Finally, the Coast Guard could grant the city's request to restrict bridge openings.

The transportation agency says the aforementioned warning signs allow many driver to avoid being caught in the traffic jams, but noted that most of that traffic simply is diverted to the West Seattle Bridge, adding to traffic delays getting onto State Route 99 and onto the Interstate 5 freeway.

Delays because of bridge openings this year have remained about average, the city told the Coast Guard. There were 11 morning openings in January and 9 in February with average opening times of 14 minutes in January and 12 minutes in February. Similar numbers were reported in the afternoon.

The Coast Guard must publish the city's request in the Federal Register, probably this week. Then the public has a 60-day comment period, following a Coast Guard decision on the matter.

Jack Mayne may be reached at jmayne@robinsonnews.com or at 369.6328.