Complex sentence: On 8 May 2012, KMB withdrew its last non-air-conditioned buses from service, from then on all the franchised bus routes in Hong Kong were operated solely by air-conditioned buses.
Split into simpler sentences: On 8 May 2012, KMB withdrew its last non-air-conditioned buses from service. From then on, all franchised bus routes in Hong Kong have been operated solely by air-conditioned buses.