The preparation, the dress rehearsals, the warning and the pleading have come down to this: Viadoom, Seattle Squeeze, Goodbye-aduct — whatever you want to call it, Seattle’s new traffic imbroglio begins Monday, with the longest highway shutdown the region has ever seen. Monday morning marks the first weekday commute of the three-week closure of Highway 99, as construction crews race to build ramps and connect the new Highway 99 tunnel’s north and south ends to the existing roadway. Transportation officials are urging commuters to telecommute, shift their schedules, walk, bike, take the bus or the train, carpool or try the water taxi — anything but drive into work alone. “Traffic conditions [Monday] morning are going to depend on the decisions of the 250,000 people who come into the city for work or appointments,” said Heather Marx, the director of downtown mobility for the Seattle Department of Transportation (SDOT).