In 2020, the STIB achieved the renewal of its ISO 14001 certification for 3 years for all its activities, by an independent certification body. This international certification aims to encourage companies to control the impact of their activities on the environment and demonstrate the effectiveness of both the management systems and the continuous improvement of their environmental procedures, in a way that respects legal provision and takes into account the context and stakeholders.

No non-conformities were detected during the auditors' visits and interviews. Among the many positive points were the environmental clauses included in the specifications for the purchase of hybrid and electric buses, the improvement of the health and safety record management system, the network of committed environmental correspondents and the deployment of a strong internal communication campaign, "Be STIB, Be Green", with a recognisable graphic identity, and the distribution of tools, such as eco-cards and "environmental toolboxes" for workshop and garage staff.

In addition, the Marconi depot, which opened in 2018, has officially received its final BREEAM (Building Research Establishment's Environmental Assessment Method) certification, with a "very good" rating. This is the most widely used environmental building assessment method in the world. The advantages of the Marconi site include energy management, rainwater recovery and biodiversity through the planting of native plants.