In this paper, a new transport system for city logistics, based on automated vehicles, is presented. Deliveries are performed by platoons of electric and automated vehicles in which the leading one is driven while the others move driverless. Each platoon travels from the Urban Distribution Centre (UDC) to a specific place on the border of the city centre, named Split Up Location (SUL), where the platoon is divided. Then each vehicle, except for the leading one, carries out the last mile deliveries in a driverless way. Meanwhile, the driver relocates to another SUL or to the UDC, if required. After finishing the deliveries, vehicles come back to the SUL and reassemble in a platoon; a driver gets into the leading vehicle, then the platoon returns to the UDC. A methodology has been developed to design, simulate and optimize the proposed transport system. The proposed methodology is composed of: optimization algorithms for all phases of the delivery trips; an object-oriented simulator of the proposed transport system. The simulator modelizes the second-by-second activities of each platoon, each vehicle and each driver and it allows to evaluate, dynamically, the number of vehicles required to operate the system and the timetable of driver activities. The system proposed has been applied to the case study of Piraeus, Greece.