Problem. The increase in the level of motorization and in the concentration of vehicles in major cities over the past decade has led to an intensive increase in traffic on the main streets of Ukrainian cities and, as a result, the number of involuntary stops has increased, the speed of traffic flows has decreased, resulting in a cut of the traffic speed and a significant increase in the level of pollution of the environment. Improving the conditions of road traffic in modern cities requires the application of a whole complex of architectural, planning and technical measures. While the implementation of road, architectural and planning measures requires both a sufficiently long period of time and significant capital investments, traffic management measures can provide an immediate effect, and in some cases these measures are the only means of solving transport problems in conditions of limited territorial resources of cities. Purpose. The goal is an analytical and experimental assessment of the delay time at a controlled intersection before and after expanding the phase of the left-turn traffic of the main highway in a three-phase traffic light regulation cycle on a city highway with a central median. Methodology. An analytical approach has been used for developing a model of the delay of vehicles at a controlled intersection, the adequacy of which has been assessed with a simulation experiment conducted in the Vissim software environment using as an example the city highway with a central median. Results. It has been established that the created analytical dependence of the delay of vehicles at a controlled intersection has a narrow field of use that is only at low levels of loading the lane of traffic. This makes it clear that there is a need to develop the delay models that give an adequate valuation of the delay for all levels of loading. The proposed extension of the phase of the left-turning traffic flow is a common solution for similar traffic lights objects and can significantly reduce the waiting time. Novelty. The developed analytical model is based on generally accepted driving conditions at isolated controlled intersections, but it is completely original. The quantitative estimation of the effectiveness of the given improvement of the traffic light cycle has been obtained for the first time. Practical value. The proposed and justified improvement of the traffic light cycle can significantly reduce the delays of vehicles at controlled intersections with a three-phase traffic light control cycle, similar to the one considered in the paper.