A lockout of union longshoremen at 29 West Coast ports sent immediate ripples through the US economy yesterday, threatening the motor vehicle industry, a Reuters report said. According to Reuters, port employers said the indefinite lockout could cost the economy as much as $US1 billion a day, was spurred by the International Longshore and Warehouse Union, whose 10,500 members  have been working without a contract since July 1, and have denied slowing shipments as a negotiating ploy