The Mixed Economy in the Islamic System

The main road networks, the main rail networks, oil, gas, electricity, water are public property which need to be administered by the state on behalf of the people. So we established that that is a mix, what some people call a mixed economy. How would the Islamic system then, given that it does accept a mixed economy, deal with this apparently intrinsic tendency to concentration of monopoly power in the system? That was kind of my question.