In this paper, we establish an activitybased behavioral model for a specific flexible working arrangement (FWA) which is composed of core and flexible working times. The proposed behavioral model is distinguished from the traditional model with flexible parameters. Both analytical and simulationbased approaches are employed to analyze the impacts of FWA with different percentages of flexicommuters on the departure patterns and delays. The results show that FWA has positive effects on relieving congestion. The average travel time decreases with the increasing percentages of flexicommuters, especially for fixedtime commuters. However, the effects diminish gradually.