Overall health impacts of a potential increase in cycle commuting in Stockholm, Sweden.

AIMS: To estimate the overall health impact of transferring commuting trips from car to bicycle. METHODS: In this study registry information on the location of home and work for residents in Stockholm County was used to obtain the shortest travel route on a network of bicycle paths and roads. Current modes of travel to work were based on travel survey data. The relation between duration of cycling and distance cycled was established as a basis for selecting the number of individuals that normally would drive a car to work, but have a distance to work that they could bicycle within 30 minutes. The change in traffic flows was estimated by a transport model (LuTrans) and effects on road traffic injuries and fatalities were estimated by using national hospital injury data. Effects on air pollution concentrations were modelled using dispersion models. RESULTS: Within the scenario, 111,000 commuters would shift from car to bicycle. On average the increased physical activity reduced the one-year mortality risk by 12% among the additional bicyclists. Including the number of years lost due to morbidity, the total number of disability adjusted life-years gained was 696. The amount of disability adjusted life-years gained in the general population due to reduced air pollution exposure was 471. The number of disability adjusted life-years lost by traffic injuries was 176. Also including air pollution effects among bicyclists, the net benefit was 939 disability adjusted life-years per year. CONCLUSIONS: Large health benefits were estimated by transferring commuting by car to bicycle.

Potential Effects on Travelers' Air Pollution Exposure and Associated Mortality Estimated for a Mode Shift from Car to Bicycle Commuting.

This study aims to use dispersion-modeled concentrations of nitrogen oxides (NOx) and black carbon (BC) to estimate bicyclist exposures along a network of roads and bicycle paths. Such modeling was also performed in a scenario with increased bicycling. Accumulated concentrations between home and work were thereafter calculated for both bicyclists and drivers of cars. A transport model was used to estimate traffic volumes and current commuting preferences in Stockholm County. The study used individuals' home and work addresses, their age, sex, and an empirical model estimate of their expected physical capacity in order to establish realistic bicycle travel distances. If car commuters with estimated physical capacity to bicycle to their workplace within 30 min changed their mode of transport to bicycle, >110,000 additional bicyclists would be achieved. Time-weighted mean concentrations along paths were, among current bicyclists, reduced from 25.8 to 24.2 µg/m3 for NOx and 1.14 to 1.08 µg/m3 for BC. Among the additional bicyclists, the yearly mean NOx dose from commuting increased from 0.08 to 1.03 µg/m3. This would be expected to yearly cause 0.10 fewer deaths for current bicycling levels and 1.7 more deaths for additional bicycling. This increased air pollution impact is much smaller than the decrease in the total population.

Impacts on air pollution and health by changing commuting from car to bicycle.

Our study is based on individual data on people's home and work addresses, as well as their age, sex and physical capacity, in order to establish realistic bicycle-travel distances. A transport model is used to single out data on commuting preferences in the County Stockholm. Our analysis shows there is a very large potential for reducing emissions and exposure if all car drivers living within a distance corresponding to a maximum of a 30min bicycle ride to work would change to commuting by bicycle. It would result in >111,000 new cyclists, corresponding to an increase of 209% compared to the current situation. Mean population exposure would be reduced by about 7% for both NOx and black carbon (BC) in the most densely populated area of the inner city of Stockholm. Applying a relative risk for NOx of 8% decrease in all-cause mortality associated with a 10µgm-3 decrease in NOx, this corresponds to >449 (95% CI: 340-558) years of life saved annually for the Stockholm county area with 2.1 million inhabitants. This is more than double the effect of the reduced mortality estimated for the introduction of congestion charge in Stockholm in 2006. Using NO2 or BC as indicator of health impacts, we obtain 395 (95% CI: 172-617) and 185 (95% CI: 158-209) years of life saved for the population, respectively. The calculated exposure of BC and its corresponding impacts on mortality are likely underestimated. With this in mind the estimates using NOx, NO2 and BC show quite similar health impacts considering the 95% confidence intervals.

Potential health impacts of changes in air pollution exposure associated with moving traffic into a road tunnel.

A planned 21 km bypass (18 km within a tunnel) in Stockholm is expected to reduce ambient air exposure to traffic emissions, but same time tunnel users could be exposed to high concentrations of pollutants. For the health impacts calculations in 2030, the change in annual ambient NOX and PM10 exposure of the general population was modelled in 100 × 100 m(2) grids for Greater Stockholm area. The tunnel exposure was estimated based on calculated annual average NOX concentrations, time spent in tunnel and number of tunnel users. For the general population, we estimate annually 23.7 (95% CI: 17.7-32.3) fewer premature deaths as ambient concentrations are reduced. At the same time, tunnel users will be exposed to NOX levels up to 2000 µg/m(-3). Passing through the whole tunnel two times on working days would correspond to an additional annual NOX exposure of 9.6 µg/m(3). Assuming that there will be ~55,000 vehicles daily each way and 1.3 persons of 30-74 years of age in each vehicle, we estimate the tunnel exposure to result in 20.6 (95% CI: 14.1-25.6) premature deaths annually. If there were more persons per vehicle, or older and vulnerable people travelling, or tunnel dispersion conditions worsen, the adverse effect would become larger.