Merging of traffic flows is a potentially dangerous situation frequently associated with important impacts on traffic fluidity. This paper examines the possibility of improving merging from an entrance of a highway by adapting the speed of the incoming vehicles reducing as much as possible the need for actions by the drivers on the main lane. Multi-layer traffic models are used to describe and simulate the interactions between drivers. A predictive controller is then designed to minimize the probability that the vehicles on the incoming roads need to change the speed or the lane. The proposed approach is shown to strongly enhance traffic fluidity for a wide range of traffic densities on the main flow without compromising safety.