People ride bikes on Car Free Sunday in Brussels, Belgium, Sept. 19, 2021. The Car Free Sunday is valid for the public, except taxis, journey buses, emergency services, police and persons with a special permit. The whole Brussels Region is closed for traffic from 9:30 a.m. till 7 pm. Photo: Xinhua

People ride bikes on Car Free Sunday in Brussels, Belgium, Sept. 19, 2021. The Car Free Sunday is valid for the public, except taxis, journey buses, emergency services, police and persons with a special permit. The whole Brussels Region is closed for traffic from 9:30 a.m. till 7 pm. Photo: Xinhua

People ride bikes on Car Free Sunday in Brussels, Belgium, Sept. 19, 2021. The Car Free Sunday is valid for the public, except taxis, journey buses, emergency services, police and persons with a special permit. The whole Brussels Region is closed for traffic from 9:30 a.m. till 7 pm. Photo: Xinhua

People ride bikes on Car Free Sunday in Brussels, Belgium, Sept. 19, 2021. The Car Free Sunday is valid for the public, except taxis, journey buses, emergency services, police and persons with a special permit. The whole Brussels Region is closed for traffic from 9:30 a.m. till 7 pm. Photo: Xinhua

People ride bikes on Car Free Sunday in Brussels, Belgium, Sept. 19, 2021. The Car Free Sunday is valid for the public, except taxis, journey buses, emergency services, police and persons with a special permit. The whole Brussels Region is closed for traffic from 9:30 a.m. till 7 pm. Photo: Xinhua

People ride bikes on Car Free Sunday in Brussels, Belgium, Sept. 19, 2021. The Car Free Sunday is valid for the public, except taxis, journey buses, emergency services, police and persons with a special permit. The whole Brussels Region is closed for traffic from 9:30 a.m. till 7 pm. Photo: Xinhua