Interaction among vehicles based on wireless communication technologies is an efficient way to improve traffic conditions and safety. In this context, The Grand Cooperative Driving Challenge (GCDC) is an event that aims at developing cooperative systems for intelligent vehicles. Although the two editions of the event (2011 and 2016) have provided conditions for a series of experiments such as platoon stability and lane-merging, the traffic flow in lane-merging scenarios didn't receive so much attention. This paper presents a preliminary study on traffic flow using GCDC 2016 interaction protocol for lane-merging by varying the driver imperfection model and the number of vehicles. We also propose an extension of the standard protocol. We evaluated three lane-merging interaction protocols using the Simulation of Urban Mobility (SUMO). The first protocol is very similar to the GCDC 2016, the second is the default lane change model commonly used in SUMO and the third is a variation of the GCDC interaction protocol. The experiments were conducted using similar conditions and number of vehicles of the event. We analyzed the lane-merging total time for all vehicles to complete the maneuver, the maximum string platoon length and the average platoon speed. Therefore, we could observe that the interaction protocol extension proposed decreased the duration time to complete the lane-merging maneuver of all vehicles without drastically compromising maximum string length and average platoon speed. The flexibility of this extension is closer to real traffic scenario, in which vehicles can perform the merge without having a pre-defined order.