Switzerland's largest city on Monday launched a new dimension in drive-through services: prostitution. In an effort to move the sex trade from central Zurich's banking and business districts, city officials have built a cluster of garagelike "sex boxes." A motorist in search of a tryst can troll past a sidewalk lined with licensed hookers and drive the one of his choosing to the relative privacy accorded by three wooden walls. Prostitution has been legal in Switzerland since 1942, and the financial capital of the federation has long had an active flesh trade. Zurich officials and city business leaders led the campaign to create the new car-sex complex at the edge of town to better protect prostitutes and prevent their being drawn into drugs and other illegal activities that plague the urban center. Zurich officials praised the project, built for $400,000 less than the voter-approved $2.6 million budget.