New Zealand-based bus manufacturer DesignLine, which already has three 37-seater vehicles valued at $784,000 operating as part of a pilot scheme in New York City, may be joined by 87 more buses by the end of the year. The newest addition to New York City’s formidable bus fleet – the experimental DesignLine turbine hybrid – is notable mainly for a feature it does not have: noise. “Quiet as a tomb,” declared Doreen Frasca, an appointee to the board of the Metropolitan Transportation Authority, who has taken the bus several times in the last month. Silence, that rare commodity on the city streets, is achieved by throwing out the most basic element of automobile design: internal combustion. Instead of a noisy, piston-based engine, the DesignLine operates on a spinning turbine that recharges a lithium-ion battery, a green energy source more commonly found inside laptop computers. That means fewer moving parts, and fewer ways to create a racket. DesignLine International Holdings employs between 13 and 15 people in Ashburton and last year set up a second manufacturing plant in Charlotte, North Carolina. New Zealander John Turton started the business 23 years ago but sold out to a North Carolina-based investment group in 2006.