People ride bicycles as they enjoy a car-free day in Brussels, at the occasion of the week of mobility, on September 16, 2018. - Europe should hold an annual car-free day in a bid to ease air pollution, the mayors of Paris and Brussels said on September 15, 2018 on the eve of a vehicle-free day in their cities. (Photo by HATIM KAGHAT / BELGA / AFP) / Belgium OUT        (Photo credit should read HATIM KAGHAT/AFP via Getty Images)