Mobile Internet applications, such as smartphones, have been widely popularized in China. The smartphones' GPS localization, map navigation functions, etcetera, have brought great convenience to traffic travel. However, the application of smartphones also has a tremendous impact on the operation of the traffic systems. This thesis mainly studies the influence of drivers-and-pedestrians' smartphone use on traffic efficiency and traffic safety at signalized intersections. Selecting typical signalized intersections in Hangzhou, China, as the research object, the thesis carries out the research from two perspectives (vehicle capacity and pedestrian safety), and answers the following five research questions: (1) Investigation of driver mobile phone use during the red traffic signals, (2) Analysis of the influencing factors of driver's phone use behavior during the red traffic signal, (3) Analysis of the impact of mobile phone use on start-up loss time, headway and saturation flow at the intersection, (4) Assessment performance indicators of pedestrian crossing behavior, and (5) Analysis of the influence of mobile phone use on the safety of pedestrian crossing behavior.