Complex sentence: The Mercedes-Benz O530LE Citaro is the standard single deck vehicle in the fleet, with 12 of these vehicles entering service in 2011, with another dozen entering service between April and May 2012.
Split into simpler sentences: The Mercedes-Benz O530LE Citaro is the standard single deck vehicle in the fleet. Twelve of these vehicles entering service in 2011 whilst another dozen entered service between April and May 2012.