The delivery of parcels in city centers is nowadays a topical issue and a major challenge for the local authorities. In this paper, we tackle the parcels distribution network in the city of Bordeaux. This city is at the very beginning of the process of moving from direct deliveries towards city center, to a more rational organization based on joint deliveries. We focus on the potential contributions of a two-tier distribution system made up of warehouses, proximity logistics spaces and intermediate depots so-called urban consolidation centers (UCCs). We seek to optimize the costs of the distribution network (i.e. transport and UCCs) and the selection of UCCs, while assessing the impact in terms of sustainable development by measuring CO2 emissions. We analyze and compare different scenarios using different deliveries' variants (with or without UCCs), different total UCCs capacities and different truck speeds. The findings demonstrate the benefits of using UCCs for city center distribution. The reductions in total cost and CO2 are most significant when the size of the UCCs is balanced with the total deliveries demands.