Hoping to cast some light on the issue, a group of Lower Manhattan residents is preparing to sue the New York Police Department over its security plan for the World Trade Center, saying that the plan will leave the center in “fortresslike isolation” and the area around it “as impervious to traffic as the Berlin Wall.” … The Police Department plans to close the streets in and around the trade center to normal through traffic. Vehicles would be screened before entering this zone, or “campus,” as the police call it. Some would be searched. Only those having demonstrable business at the trade center, or those previously certified as trustworthy, would be allowed in.