The 77-year-old pontiff recalled that for his July 2013 visit to Brazil officials had prepared a glass-enclosed "popemobile" to shield him.
"But I cannot greet the people and tell them I love them inside a sardine can, even if it is glass," he said in an interview with the Barcelona-based Vanguardia newspaper.
"For me it is a wall," said the spiritual leader of the world's 1.2 billion Roman Catholics.
"It is true something could happen to me but let's be realistic, at my age I do not have much to lose," he told the paper's Vatican correspondent Henrique Cymerman.
"It is in God's hands."
Francis has preferred to use open-top cars in contrast to his predecessor Benedict XVI who rode in a bulletproof "popemobile" - a novelty introduced after the attempted assassination of John Paul II in 1981.
But concerns over the pontiff's safety were raised last year after an Italian prosecutor warned the country's mafia bosses were becoming "upset" and may "trip him up". Nicola Gratteri said the Calabria region's 'Ndrangheta mafia was frustrated with the Pope's reform of the Vatican's financial bodies.