Complex sentence: The full service buffet car was replaced with a buffet servery, both measures significantly reduced costs, but the service was challenged by the increasing number of low cost shuttle bus services, particularly between Christchurch and Dunedin, which were significantly cheaper than the train.
Split into simpler sentences: The full service buffet car was replaced with a buffet servery. Both measures reduced costs significantly, but the service was challenged by the increasing number of low-cost shuttle bus services, particularly between Christchurch and Dunedin, which were significantly cheaper than the train.