In this study, changes in traffic flow characteristics were examined in a mixed system consisting of human drivers and autonomous vehicles. In the study, it is accepted that in the environment where the autonomous vehicles are presented, neither vehicle to vehicle communication (V2V) nor the environment and infrastructure communication of vehicles (V2I) exist. The behavioral characteristics of human drivers (reaction time, acceleration, and deceleration, etc.) are derived from data collected from field studies, while the characteristics of autonomous vehicles are determined on the basis of assumptions in literature. Using these data together, the behaviors of the different driver profiles and the movements of the autonomous vehicles under the same conditions are compared by using the SIDRA TRIP program. By using the outcomes of the program and producing different scenenarios, a passenger car equivalence value for autonomous vehicles was tried to be obtained. In the last section of the study, the effect of autonomous vehicles on signalized intersection performance in an unconnected environment is discussed. The results show that autonomous vehicles may significantly decrease intersection capacity.

Although many traffic circles have been designed in Turkey, in recent years few studies have been made on the capacity and performance of roundabouts. In practice, two major problems at intersections need to be solved: traffic accidents and limited intersection capacity. With this in mind, the applicability of various capacity models for single-lane roundabouts to six selected roundabouts in Izmir, Turkey, is discussed. The results show that the HCM2000 procedure can be used as an effective tool for an initial prediction of single-lane roundabout capacity if the lower and upper boundary limits are calibrated. But, since the research was conducted with limited data, the accuracy of the results should be tested with more data sets. Further studies should be conducted to develop a more reliable capacity and performance analysis procedure, especially for Turkey.

Induced travel demand is a critical phenomenon for developing countries because neither road network nor the vehicle ownership have reached their contended phases. This leads to the opinion that induced demand is valid for developing countries or increase in travel demand is only a result of rapidly rising vehicle numbers and other socioeconomic parameters. In this study, induced demand estimation methodology is modified from the point of view of a developing country by introducing the application of tendency comparison of lane mile elasticities under different lag terms for control and highway investment data. Beside vehicle miles traveled, travel per vehicle (TPV) and number of vehicles for long-term effects are tried as new demand indicators. The selection of socioeconomic variables is also considered more expediently because of their rapid and wide changes in developing countries. The travel data of Turkish state highways are used for application. TPV is found to be the most distinguishable criterion of induced travel demand for Turkey with 2.0 times relative increase for private TPV and 3.5 times for commercial TPV. Demand elasticities based on commercial travel are found to be more permanent than the private travel based ones. Besides, longer peak period, which indicates the maximum difference in elasticity of control and test data, is obtained as $5\text{years}$ for commercial travel which is $3\text{years}$ for private purposed travel in lag consideration based on road supply conditions.

Although traffic circles have been widely used in Turkey for many years, only a few researchers are aware of the advantages of roundabouts. In recent years, few traffic circles were designed as roundabouts in Turkey, but limited study has been made on the capacity and performance analysis of roundabouts. In this study, the applicability of the Highway Capacity Manual 2000 (HCM 2000) procedure for roundabouts in Turkey is discussed. The results show that the HCM 2000 procedure can be an important tool for an initial prediction but further studies should be made in order to develop a more reliable capacity and performance analysis procedure for Turkey.

The studies on headway characteristics of traffic flow in Turkey are mainly dealing with signalized arterials, intersection approaches or roundabouts. Only a few studies can be found on headway characteristics of uninterrupted flow facilities and nearly none of them are on lane by lane basis. In this study, the authors are modeling headways of vehicles at zmir ring roads by lane by lane principle. The study demonstrates that lognormal distribution is an effective tool to define headways. In addition, the applicability of Cowan M3 distribution to time headways is investigated. Proportion of free vehicles is modeled for different lanes. The results show that traffic flow in the middle lane is highly affected by the vehicles in other lanes. Vehicles in the outer lane can be assumed to arrive randomly, but they are also disturbed by vehicles in other lanes. These results can be used in capacity and performance analysis of freeway segments, ramp junctions and weaving areas.