A new fully air-conditioned bus interchange in Boon Lay will open during the year-end school holidays.At 20,000 sq m and costing $24 million, it will be Singapore's biggest and most expensive bus interchange to date. It will also have the most number of bus services, with 31 in all.When open, Boon Lay will be the fourth town to have an integrated public transport hub, in which the bus interchange and MRT station are seamlessly linked together with retail outlets.The other integrated hubs are in Toa Payoh, Ang Mo Kio and Sengkang, while Clementi and Serangoon are expected to get air-conditioned bus interchanges in 2011.