Thanks to growing ridership, New York City is bringing back the double-decker bus for a 30-day trial period starting tomorrow. The sleek new coaches will be in service along the "BxM3 from Yonkers to Manhattan, the X17J between Staten Island and Manhattan, the M15 limited on First and Second Avenues, and possibly the M5 along Fifth Avenue." If the test goes smoothly, the buses might return for good.This would be great for the efficiency of public transportation in New York. Each bus costs $650,000 each which, while initially shocking, is actually less than the mind-blowing $900,000 the city pays for the articulated buses in use today. The buses also capitalize on that available vertical real estate and run on ultra low sulfur diesel, lowering the M.T.A.'s overall carbon footprint.Howard H. Roberts Jr., president of New York City Transit, sounds serious about the initiative. At yesterday's press conference he said "This is not just a show... It's not a movement to titillate the public." We know, Howard, but we can't help it. Double-decker buses just have that effect on us.