Background: Bicycle commuting in an urban environment of high air pollution is known as a potential health risk, especially for susceptible individuals. While risk management strategies aimed to reduce motorised traffic emissions exposure have been suggested, limited studies have assessed the utility of such strategies in real-world circumstances.Objectives: The potential of lowering exposure to ultrafine particles (UFP; < 0.1 mum) during bicycle commuting by reducing proximity to motorised traffic was investigated with real-time air pollution and intermittent acute inflammatory measurements in healthy individuals using their typical, and an alternative, bicycle commute route. Methods: Thirty-five healthy adults (mean +/- SD: age = 39 +/- 11 yr; 29% female) completed two return trips, one each of their typical route (HIGH) and a pre-determined alternative route of lower proximity to motorised traffic (LOW; determined by the proportion of on-road cycle paths). Particle number concentration (PNC) and diameter (PD) were monitored in-commute in real-time. Acute inflammatory indices of respiratory symptom incidence, lung function and spontaneous sputum (for inflammatory cell analyses) were collected immediately pre-commute, and one and three hours post-commute. Results: In LOW, compared to HIGH, there was a significant decrease in mean PNC (1.91 x e4 +/-
0.93 x e4 ppcc vs. 2.95 x e4 +/- 1.50 x e4 ppcc; p <= 0.001), the incidence of in-commute offensive odour detection (42 vs. 56%; p = 0.019), and the incidence of dust and soot observation (33 vs. 47%; p = 0.038) and nasopharyngeal irritation (31 vs. 41%; p = 0.007). There were no significant differences between LOW and HIGH in the commute distance and duration (12.8 +/- 7.1 vs. 12.0 +/- 6.9 km and 44 +/- 17 vs. 42 +/- 17 min, respectively), or indices of acute airway inflammation. Conclusions: Exposure to PNC (and the incidence of offensive odour and nasopharyngeal irritation) can be significantly lowered when utilising a route of reduced proximity to motorised traffic whilst bicycle commuting (without significantly affecting commute distance or duration), which may bring important benefits for both healthy and susceptible individuals.