Assessment of bus service improvements such as bus lanes, allowing boarding through all doors and headway-based holding control ideally requires a simulation model that combines features of both classical analytical models and microscopic simulation. However, as the usage of such models has been limited, their validity has hitherto remained low. BusMezzo, a dynamic transit operations and assignment model, was developed to enable the analysis and evaluation of transit performance and level of service under various system conditions. This paper describes two case studies where assessment of bus service improvements in BusMezzo was tested and validated. The model was shown to predict travel time improvements well, while overestimating some of the headway variability effects. It turned out that the preferential measures had a positive system impact and that there are synergetic effects.