I am in favor for more environmental friendly buses but based on current technologies, cost of operations and avaliability of infrastructure, it will still need to take another 5 to 10 years more before we can really see them.
Even on the current hybrid car technologies, there are still many teething problems for hybrid technologies and the cost of manufacture, operating is still higher than conventional petrol and diesel cars. Moreover unlike other countries, Singapore government only talk and talk about caring for the environment but actions on incentives to bring in such vehicles seems to be slow, slow introduction of such cars, inadequate tax incentives and infrastructure, etc. Even Frisker cars, manufacturer of electric cars, which wanted to sell full electric cars here by this year hits the speed bump. The relevant local authorities gave a very lame excuse that the technology is currently still not suitable here or something like that.
However bio diesel will be another better alternative as it is as cheap as petrol and diesel, doesn't require much changes to current engine technologies, easily obtainable (from used cooking oil and hence recyclable too, and through growing of plants which provide bio fuel), and most importantly, much lower emissions than conventional fuels. However the technologies of refining bio diesel needs to be further improved to reach the efficiency standards of diesel.