Background: We aimed to quantify the number of women and men, in Catalonia, among those not achieving physical activity recommendations, making short motorized trips which could have been made on foot, and to estimate the annual economic benefit due to reducing mortality as a result of replacing one short, daily, motorized journey with walking. Methods: Cross-sectional study. Mobility data came from individuals >17 years who reported, in the 2006 Daily Mobility Survey, having travelled on the referred working day (N = 80 552). The health economic assessment tool for walking (HEAT) from the World Health Organization (WHO) Regional Office for Europe was used to calculate the economic benefit. Results: Of those not meeting recommendations, 15.6% of men (95% CI 15.2–16.1) and 13.9% of women (95% CI 13.5–14.4) would go on to meet them if they were to replace at least one short motorized trip per day by walking. If applied to the entire population of Catalonia, this change would increase up to 326 557 men (95% CI 313 373–339 740) and up to 252 509 women (95% CI 240 855–264 163) who would achieve recommendations through walking rather than driving. According to HEAT estimations, this would suppose a saving of €124 216 000 (95% CI 120 182 000–128 250 000) in men and €84 927 000 (95% CI 81 774 000–88 079 000) in women, derived from the reduction in mortality gained from walking accumulated over one year. Conclusion: This study demonstrates the potential of trips on foot as a source of physical activity. It also points out that both benefits for the health of the population and a huge economic benefit could have been gained through active transportation interventions.