As the leading state-owned construction company in Indonesia, PT Adhi Karya (Persero) Tbk (ADHI) has taken certain steps to address sustainability issues, especially when it comes to improving the environmental quality of infrastructure projects. "WE R GREEN" is an environmental program that emphasizes water conservation (W), energy efficiency (E), waste management (R, which stands for remove, reduce, reuse, and recycle), and tree planting activity (GREEN). This study used a construction project in Depok as the sample, where every action has a close relationship with the environment. The purpose of this study is to determine the CO2 efficiency of some project activities following the implementation of the "WE R GREEN" initiatives. The data consists of water consumption, project office building usage, electricity consumption, solid waste production, and planted tree specification. According to the data, total CO2 emissions were 110,62 tons CO2e year prior to program implementation, and the emission has dropped to 73,59 tons CO2e annually following the initiatives. This concludes that the total of 37,03 tons CO2e per year, or 33%, are reduced. Assuming the same number of people and project activities throughout all 109 ADHI projects to put the program into practice. The estimated annual CO2 output would thus decrease 4.036,06 tons CO2e.