In value-based transmission planning, market efficiency and associated economic benefits can be achieved from transmission solutions that reduce system congestions. However, to accrue the most value and design the most cost effective transmission solution, it is beneficial to understand the interactions among congested flowgates and strategically address selected congestion issues collectively rather than individually. This paper proposes two methods to group congested flowgates: correlation method and OTDF method. The proposed methods have been applied to MISO system to demonstrate the effectiveness. Simulation results using hourly chronological SCUC/SCED tool show that up to 370% synergic benefits can be realized if identified groups of congested flowgates are addressed at the same time. The proposed methods are easy to implement, and have great computational advantage over existing simulation-based exhaustive method.