Cyclists' exposure to air pollution, noise, and greenery: a population-level spatial analysis approach

Abstract

Urban travel exposes people to a range of environmental qualities with significant health and wellbeing impacts. Nevertheless, the understanding of travel-related environmental exposure has remained limited. Here, we present a novel approach for population-level assessment of multiple environmental exposure for active travel. It enables analyses of (1) urban scale exposure variation, (2) alternative routes' potential to improve exposure levels per exposure type, and (3) by combining multiple exposures. We demonstrate the approach's feasibility by analysing cyclists' air pollution, noise, and greenery exposure in Helsinki, Finland. We apply an in-house developed route-planning and exposure assessment software and integrate to the analysis 3.1 million cycling trips from the local bike-sharing system. We show that especially noise exposure from cycling exceeds healthy thresholds, but that cyclists can influence their exposure by route choice. The proposed approach enables planners and individual citizens to identify (un)healthy travel environments from the exposure perspective, and to compare areas in respect to how well their environmental quality supports active travel. Transferable open tools and data further support the implementation of the approach in other cities.

Keywords: Active travel; Air pollution; Environmental exposure; Greenery; Noise; Route choice.

Fig. 1

Example bikes of the Helsinki bike-sharing system. Photo by the authors

Fig. 2

Flow chart of the analytical process

Fig. 3

Spatial variation of average trip exposure to air pollution, noise, and greenery aggregated to the bike-sharing station catchment areas. Catchment area represents the area, in which the given station is closer than any other station measured by Euclidean distance. The maps on the left side show the variation for the shortest routes, the maps on the right side show the spatial variation for the exposure-optimal routes over the study area. The black dots on the map show the locations of bike-sharing docking stations

Fig. 4

The distribution of air pollution, noise, and greenery exposure values for all bike-sharing system routes along the shortest and the exposure-optimal route. Non-trip-weighted distributions are shown on the left and trip-weighted on the right

Fig. 5

The distribution of detour distances (%) of the exposure-optimal routes compared to the shortest routes for all bike-sharing system origin–destination pairs. On the left, the charts show the distribution for non-trip-weighted routes, in the middle, the distribution for the trip-weighted routes is shown, and on the right, the improvements in average route exposures are plotted against the proportional detour distances. The bars display the detour distance distribution of all alternative exposure routes without any distance threshold, while the black dotted lines display the 15% detour distance threshold that we used in the comparative analyses in this study

Fig. 6

Average proportion of shared route between air quality, noise, and greenery-optimal routes (trip-weighted) over the study area. The common shares by route are aggregated to the bike-sharing station catchment areas

Fig. 7

The relationship between air pollution, noise, and greenery values for bike-sharing system routes. On the left, the relationship along the shortest routes is displayed and on the right the relationship along the exposure-optimal routes. The exposure values are aggregated to the mean over the x-axis, and the 95% confidence interval is displayed as a line. In addition, the Pearson correlation coefficient is shown

Fig. 8

The count of departing bike-sharing trips by the bike-sharing docking station catchment area in 2019 in Helsinki. The catchment areas are delineated with Voronoi polygons

Fig. 9

The distribution of Air Quality Index (AQI), noise and Green View Index (GVI) values over the study area

Fig. 10

The spatial variation in opportunities to improve air quality, noise, and greenery exposure with a route choice in cycling trips. The values, which are aggregated to the bike-sharing station catchment areas, represent the average difference (trip-weighted) in air quality, noise, and greenery exposure between the shortest route and the exposure-optimal route. The black dots on the map show the locations of bike-sharing stations

Fig. 11

The distribution of shared route percentage between the air quality, noise, and greenery optimal routes for all origin–destination pairs. The charts on the left show the non-trip weighted distribution and the charts on the right show the trip-weighted distribution of shared route percentage. The highest bars at the ends of the x-axis correspond to the situation where exposure-optimal route is not available for the given origin–destination pair and therefore the shortest route is used