1 From the aInstitute for Transport Studies, University of Leeds, Leeds, United Kingdom; bInstitute for Risk Assessment Sciences, Utrecht University, Utrecht, The Netherlands; cISGlobal, Centre for Research in Environmental Epidemiology (CREAL), Barcelona, Spain; dDepartment of Urban and Regional Planning and Geo-Information Management, University of Twente, Enschede, The Netherlands; eUniversitat Pompeu Fabra (UPF), Barcelona, Spain; and fCIBER Epidemiología y Salud Pública (CIBERESP), Madrid, Spain.