In Strava Metro, carbon savings estimates are calculated from activities tagged or identified as commutes. Commutes in Strava Metro are utilitarian trips completed on a bike or on foot, and are identified either by a Strava user tagging their activity as a commute, or by being automatically detected as such. You can find more information about Commutes on Strava in this Help Center article.
The "Estimated CO2 Saved" chart in the Metroview Dashboard displays the estimated carbon emissions savings in kilograms, as compared to completing the same trip via the average personal passenger vehicle. These estimates are based on data from the 2021 US Environmental Protection Agency (EPA) report. While individual factors may influence carbon emissions, this estimation serves as a guideline for understanding the impact of choosing human-powered transportation.
To learn more about carbon savings estimates on commutes in the Strava application, read this article from Strava Help & Support.