Comparison of Ultrafine Traffic Particle Exposures of Pupils Commuting to School by Car or Walking

Abstract

SS6-12 Introduction: Traffic congestion occurs frequently in school areas, especially during the morning hours when many parents drive their children to school by car, causing problems in the traffic flow, and increasing injury risks and air pollution exposures of the children, drivers, and residents. Ultrafine particles are a good indicator of local traffic and are suspected to cause health risks due to their combustion origin and small size. To support development of science-based environmental policies and to protect the public from unnecessary environmental risks, the current work evaluates the effects of commuting to school by walking versus by car to the exposures of school children to these particles. Material and Methods: Ultrafine particle measurements and a database of 1222 journeys of 374 pupils during 422 diary days was used in the modeling. Six hundred fifty-one trips were done to or from school. Commuting by car and walking represent together 94% of school journeys, with the remainder being divided rather evenly among school buses, taxis, buses, and cycling. School distances of 0.5 to 2 km representing 45% of pupils were selected for the current work to compare situations in which the parents have a realistic choice for taking their children to school. Daily exposures of the children living within this range from the school were modeled for the 2 commuting options. Results: Average home-school distance in the 10 schools in Leicester for all pupils living 0.5 to 2 km from their school was 0.9 km, amounting to daily commuting distance of 1.8 km. Commuting this distance by car (average speed, 30 km h-1) results in 3.6 minutes and by walking (speed 3 km h-1), 36 minutes daily (0.25 and 2.5% of daily time, respectively). Daily average exposures to ultrafines are increased from less than 3000 to almost 4000 particles per cubic centimeter, a 1.25-fold increase. Discussion and Conclusions: For short distances, the use of a car does not provide a benefit over walking, and any policy supporting not using cars for overly short distances can be highly recommended to avoid unnecessary traffic in the congested school areas. For long distances, the attractiveness of walking as a commuting option reduces quickly. Time spent in traffic increases ultrafine particle exposures rapidly. Children living in distances from school suitable for both walking and being transported by car would experience 25% higher exposures if walking. Moreover, inhalation rates are higher during walking, leading to increased intake of particles. Filtration of particles by the car ventilation system was not accounted for.