Mysterious vibrations are contributing to electrical problems that have caused a rash of recent delays for traffic on the Woodrow Wilson Bridge, officials said yesterday.
District public works officials, who are responsible for bridge operations, thought they had fixed years of electrical problems with the busy bridge when they rewired the Wilson last year.
Now a new gremlin has appeared. George W. Schoene, the city's chief traffic engineer, said the problem starts with unexplained vibrations that are damaging the new wiring.
The bridge carrying the Capital Beltway over the Potomac River between Alexandria and Prince George's County is the Washington area's worst traffic bottleneck, designed for 75,000 vehicles a day but actually crossed by some 160,000.
Twice on Sunday, the bridge was closed because of problems with the 222-foot movable drawspan. Early in the afternoon, the bridge stuck in the open position for 75 minutes and hundreds of cars backed up for two miles in both directions. Later in the day, traffic was delayed a second time when it took about 20 minutes to close the bridge.
The span is raised 400 times a year to allow tall vessels using the channel to pass through.
The drawspan also stuck open on June 26, causing long backups of traffic in both directions and calling more attention to the bridge just as federal and state officials concluded a year long contest among five engineering firms to suggest concepts for a new bridge.
But a new bridge is years away.
Schoene explained that electrical power to the drawspan is carried by wiring housed in insulated conduit. The conduit is fastened along the bridge by a series of nuts, he said.
Movement shakes loose the nuts and the conduit, causing the wiring to sag in places. That creates stress on the wiring and eventually the wire wears through or its connections pull apart and the system shorts out, Schoene said.
When the drawspan is up and a short occurs -- as was the case in the recent mishaps -- officials have no choice but to close the span manually, which takes about 20 minutes. Normally it takes an average of eight minutes for the bridge to open, a ship to pass through and the bridge to close.
Engineers have no idea what is causing the vibration, whether it is traffic, water action, wind or some other cause. Schoene and other engineers spent much of yesterday trying to identify the problem and determine whether to call in an outside expert.
Until a solution is found, he said, he is considering asking the Coast Guard to put restrictions on the time and frequency of the drawspan openings. Alexandria Mayor James P. Moran Jr. has scheduled a meeting today with Coast Guard and Federal Highway Administration officials to discuss the problem.