As the commitment of TMC (Traffic Management Centre) Polda Metro Jaya to create an orderly traffic area, Polda Metro Jaya provides interactive information to users for 24 hours per day through TMC Polda Metro Jaya's Twitter account (hereinafter referred to as TMC Polda's Twitter). To increase the effectiveness of knowledge sharing via TMC Polda's Twitter, we need to know the motivations of knowledge sharing behavior. This study investigates two-dimensional factors, which are the internal factors and external factors, that encourage users' activities to share knowledge via TMC Polda's Twitter. This study also adopts the theory of planned behavior (TPB) as a framework to understand the influence of attitudes toward knowledge sharing behavior. The respondents of this study are 416 followers of TMC Polda's Twitter. Structural equation modeling (SEM) with AMOS 22.0 tools was used to test this research. This study concludes that enjoyment in helping and information seeking are the internal factors that significantly influence the attitude of knowledge sharing, while only norm reciprocity that has positive significant influence on knowledge sharing behavior from the external factors. © 2017 IEEE.