When studied from a physiological point of view, commuting is generally divided into two categories: active and non-active. The former involves modes of transportation such as walking and bicycling, where the commuter is actively getting exercise. The latter involves modes of transportation such as cars, buses, and trains, where the commuter is getting virtually no exercise.
Many studies compare modes of transportation that fall into different categories; I chose to put them into one or the other based on which mode was focused on more. Other studies focused solely on one type of commuting. If you want to skip the specifics, you can go all the way to the bottom.
Studies on active commuting
- Hammer & Chida (2008): Commuting involving walking and bicycling corresponded to a reduction in the risk of cardiovascular diseases by approximately 11%. The effect was, for unknown reasons, more pronounced among women than among men.
- Rojas-Rueda et al. (2011): Bicyclists using a bicycle-sharing program avoided ~12.28 deaths in Barcelona over the course of one year. Some of this came from a reduction in road accidents, while other parts of it came from a reduction in carbon dioxide emissions, which reduces air quality in urban areas for commuters.
Davison et al. (2008): Children who walk and bicycle to school have, on average, better health than children who take buses or cars to school. Active transport burned 33.2-44.2 kcal per day, assuming a mean travel time for these children at about twenty minutes. Boys were more strongly effected by girls (drastically, in some cases).
Links between different types of commuting and body mass index (BMI) were tenuous at best. However, cardiovascular health was clearly raised among active commuters.
- Oja et al. (1991): Individuals who walk and bicycle for commuting have better cardiorespiratory health. However, cyclists had better health than walkers.
- Pucher et al. (2010): Health effects of commuting were studied at the city, county and state levels. Active commuting lead to a greatly lowered risk of obesity and diabetes, while improving overall cardiovascular health.
- de Hartog et al. (2011): This study took into account the potential for traffic accidents when studying commuting cyclists. It was found that the health gains far outweighed the losses from air pollution and accidents.
Studies on non-active commuting
- Nieuwenhuijsen et al. (2007): Particulate matter is abundant many metro systems (London's in particular was studied). While this may not pose a large health threat, it nonetheless may have ill effects.
- Zuurbier et al. (2010): Levels of exposure to air pollution varied with route, vehicle type, and fuel. Commuters on diesel buses were exposed to higher levels of particles than commuters on electric buses. This is in part because "self-pollution" from buses contributes a substantial fraction of all inhaled particles. However, cyclists, too, were exposed to high levels of air pollution.
- Chan et al. (2002): Transportation modes of subways, air-conditioned buses, non-air-condition buses, and taxis were studied. Commuters in non-air-conditioned buses were exposed to more particles, while commuters in subways were exposed to substantially fewer. Driving time did not seem to effect exposure.
Studies on general commuting
Hansson et al. (2011): The study cites previous studies that have shown commuting to raise stress levels under certain conditions (e.g. long travel times and crowded places). Examples are Evans & Wener (2006) and Evans & Wener (2007). Other, more complicated, effects have been observed, including loss of sleep and an increase in sick leave.
The study itself followed the population of the county of Scania, in southern Sweden. Commuters had been sent surveys that covered a variety of issues, including stress and mental health. Some correlations were found between demographics and modes of transport (which was to be expected), which most likely influenced the results. The authors found that, in general, commuters had worse sleep and lower energy. Mental health did not appear to be related.
However, given that the results were self-reported, only 56% of people responded to the survey, and there were patterns between various demographics and modes of transportation, the results are not conclusive, even given the vast number of individuals studied. Other effects may have had significant impacts.
- Roberts et al. (2011): Commuting can have negative psychological effects in women, while those same effects are not visible in men.
- Zuurbier et al. (2011): Commuters using active and passive transport may be exposed to higher levels of particulate matter from air pollution. This may cause low-level respiratory effects.
- Knibbs et al. (2011): Different modes of transportation for commuters lead to different levels of exposure to particles in the air. From least exposure to most exposure, the results were: bicycle, bus, automobile, rail, walking, and ferry. This shows a significantly higher exposure among walkers than among cyclists, meaning that active transport is not necessarily better than passive transport in this respect.
Cardiovascular health from exercise and exposure to air pollution are the two main effects of commuting, although commuting may have minor effects on stress and mental health. Cyclists and walkers had much better cardiovascular health than non-active commuters in cars, buses, trains, and subways. This may lead to lower risks of obesity and diabetes.
Exposure to air pollution varied. Commuters using the subways were exposed to different levels of different air particles than aboveground commuters. Commuters in some buses were exposed to high levels of air pollution; however, walkers and cyclists were exposed to high(er) levels in some cases. This exposure can lead to respiratory problems, although this has not yet been studied in great detail.