One of the world's most significant challenges is the effort to reduce greenhouse gas emissions. One of the primary sources of these emissions is road transport. On the other hand, road freight transport, which represents a huge portion of freight transportation, accounts for a considerable portion of the company's expenditures on fuel. Reducing fuel consumption and, therefore, greenhouse gas emissions, reducing fuel costs and increasing driving range can be achieved by increasing the energy efficiency of the vehicle. The paper presents a mathematical model for the energy-efficient control of connected, highly automated vehicles. The mathematical model incorporates terrain, speed modes, and traffic light schedules. Laboratory tests of the developed mathematical model are carried out on a digital twin of a test road section recreated on the basis of high-precision navigation data and a passenger vehicle with an internal combustion engine. In the laboratory tests, the proposed system is compared with a vehicle being driven on cruise control. The average speed of both vehicles on the selected route is identical. The results of the experimental runs indicate that the proposed mathematical model is 4.5% more efficient than the vehicle operating on cruise control. Further research is planned to adapt the developed model for hybrid and electric propulsion systems and to conduct field tests on unmanned vehicles with internal combustion engine and electric power plant.