In addition to those core cities, any city with more than 20,000 residents and episodes of high pollution also has to implement low-emission zones.
The legal details of what all of these cities have to implement are quite vague: “A low emission zone is understood as theby a Public Administration, in the exercise of its powers, within its territory, on a continuous basis, and in whichare applied to improve the quality of the air and mitigate greenhouse gas emissions, in accordance with thein accordance with the provisions of the current General Vehicle Regulations.
So, basically, the cities have to restrict access, transportation routes, or parking access in some way based on environmental classification labels . Within those boundaries, city councils have the power to decide what exact Low-Emission Zone will exist in their jurisdiction.