Double-decker buses with three sets of doors instead of the usual two will be deployed over the course of the year, the Land Transport Authority (LTA) said yesterday. A total of 100 of these buses - which cost some $64 million - will begin plying Singapore's roads, some as early as the end of this month. They will have two staircases leading to the upper deck instead of the usual one. LTA said this should improve commuter flow, with those boarding using the staircase nearer the front and those alighting using the second staircase. Those boarding the bus should continue to use the first door, but the additional exit door will allow commuters at the back of the bus to alight without having to make their way to the middle, LTA added.