The Danbury Planning Commission is opening a public hearing tonight into an application for a car dealership at Miry Brook and Sugar Hollow roads.  A stockpiling yard would be converted into a Mercedes-Benz dealership and service center if approved.  A report from the City's traffic engineers found this would generate 67 vehicle trips in the area on weekday mornings, 82 on weekday evenings, and 125 trips on a weekend days--making it a major traffic generator.  Curry Automotive recently purchased the property and plans to construct a two-story building with 250 parking spaces and 22 service bays.  Zoning variances and an environmental permit for construction have previously been approved.  The Federal Aviation Administration must still sign off on plans.