The present study develops an interfacial area transport equation applicable to an air- water horizontal bubbly flow, along which two types of horizontal elbows are installed as flow restrictions. Two sets of experiments are performed in a round glass tube of 50.3 mm inner diameter Along the test section, a 90-degee elbow is installed at L/D206. 6 from the two-phase mixture inlet and then a 45-degree elbow is installed at L/D=353. 5. In total, 15 d?fferent flow conditions in the bubbly flow regime for each of the two flow restriction experiments are studied. The detailed local two-phase flow parameters are acquired by a double-sensor conductivity probe at four different axial locations in the 90-degree experiment and three different axial locations in the 45-degree experiment. The effect of the elbows is found to be evident in the distribution of local parameters as well as in the development of interfacial structures. The elbows promote bubble interactions resulting in sign changes in both the void fraction and interfacial area concentration. These geometric effects are also reflected in the axial development of one- dimensional two-phase flow parameters. In the present analysis, the interfacial area transport equation is developed in one-dimensional form via area averaging. The mechanistic models for the major bubble interaction phenomena developed in vertical flow analysis are employed in the present study In the averaging process, characteristic non-un jform distributions of the flow parameters in horizontal two-phase flow are treated mathematically through a distribution parameter Furthermore, the change in pressure due to the minor loss of an elbow is taken into consideration by using a newly developed correlation analogous to Lockhart and Martinelli c. In total, 105 area-averaged data points are employed to benchmark the present model. The present model predicts the data relatively well with an average percent d?fference of approximately ± 20%.