Determination of highway service levels across Turkey

Level of Service is used in the evaluation of road and intersection projects in transportation systems. This concept plays a crucial role in determining practical capacity. Service level refers to the performance value of drivers and passengers regarding the traffic conditions during their journey. When assessing the service level of highways, parameters such as whether the road is urban or rural, the number of lanes, capacity, project speed, and divided or undivided nature of the road are taken into consideration. Additionally, factors such as speed, travel time, traffic flow and restrictions, maneuverability, safety, and vehicle operating costs are also taken into account. Service level is generally defined in six different categories: A, B, C, D, E, and F. A service level represents the best condition where free flow conditions are ensured, while F service level indicates the worst condition with traffic congestion. In this study, a methodology was developed to determine the service levels and bottlenecks of intercity highways throughout the country, and it was applied on the Turkey National Transportation and Logistics Master Plan transportation model. According to this methodology, density parameter was used for calculating the service level for highways, divided state roads, and divided provincial roads. For undivided state roads and undivided provincial roads, the change in free flow speed was calculated taking into account urban roads, rural roads, intersection, and intersection arms by considering traffic flow speed. In this way, the limit values that should be used in studies on service levels on highways for our country have been determined. In the light of the data obtained, the bottlenecks on intercity roads throughout our country were revealed and the highway sections that needed intervention and increased capacity were identified.