ŠTRUMBERGER, Nada; PALER, Stjepan; ŠOLMAN, Saša. Postal Operations and Environmental Protection. Promet - Traffic&Transportation, [S. l.], v. 15, n. 6, p. 387–396, 2003. Disponível em: https://traffic2.fpz.hr/index.php/PROMTT/article/view/2055. Acesso em: 26 aug. 2025.