BTEX
Abbreviations: Abs, absorbance (10 −5 m), a marker for (diesel) soot; BTEX, sum of benzene, toluene, ethylbenzene and xylene; CO, carbon monoxide; EC, elemental carbon, equivalent to (diesel) soot; TSP, total suspended dust; UFP, ultrafine particle count (per cubic centimeter).
Overall, air pollution exposures experienced by car drivers were modestly higher than those experienced by cyclists, with mean ratios of 1.16 for PM 2.5 , 1.01 for UFP, and 1.65 for elemental carbon or soot. However, increased physical activity results in higher minute ventilation (volume of air inhaled in one minute) for cyclists than for car drivers, with estimates from two Dutch studies reporting that the minute ventilation of cyclists was 2.3 times ( van Wijnen et al. 1995 ) and 2.1 times ( Zuurbier et al. 2009 ) higher than that of car drivers. Therefore, inhaled doses of PM 2.5 and, to a lesser extent, elemental carbon may be higher in cyclists. The difference in exposure between cyclists and car drivers depends on a large number of factors, such as selected route, car speed, trip duration, car type, ventilation status (open windows, mechanical ventilation), driving behavior, street configuration, and weather conditions ( Kaur et al. 2007 ). Trip duration might also be higher for cyclists, although this may be highly dependent on the setting. For example, in a study conducted in 11 Dutch cities, there was no difference in the time required to bicycle versus drive short distances ( Boogaard et al. 2009 ), but for longer trips cars were faster than cyclists ( Zuurbier et al. 2010 ).
The short exposures typical for commuting have not been studied extensively in air pollution epidemiology, in contrast to 24-hr average exposures or long-term (annual average) exposures [ World Health Organization (WHO) 2006 ]. Several studies have documented that long-term exposure to traffic-related air pollution is associated with adverse health effects, including increased mortality ( WHO 2006 ).
Table 2 summarizes the few epidemiologic studies of in-traffic air pollution exposures, suggesting that these exposures result in physiologic changes (including airway and systemic inflammation and lung function decrements) in healthy adults and asthmatics and possibly more severe adverse effects (myocardial infarction).
Epidemiological studies of air pollution exposure in traffic.
Study population | Design | Main findings | Comments | Reference |
---|---|---|---|---|
Sixty mild to moderate asthmatic adults in London | Exposure during 2 hr walking in OS or HP, pre/postexposure physiologic measurements: median PM concentration, 28 (OS) vs. 11 μg/m (HP); median EC, 7.5 vs. 1.3 μg/m ; median UFP, 63,700 vs. 18,300 particles/cm | Asymptomatic decrease in lung function and increase in inflammation after walking in OS compared with HP; changes most consistently associated with EC and UFP; per 1-μg/m significant increase in EC decrement in lung function of ~ 1% decrement in lung function and ~ 2% increase in exhaled NO (inflammation) | OS has diesel traffic only | |
Subjects ( = 691) with MI in Augsburg | Case–crossover study comparing the frequency of participation in traffic in the hours before the MI and a control period (24–72 hr before MI) | RR = 2.92 for participation in traffic in the hour before the MI; increased risk found for all transport means (car, bicycle, public transport) | May be stressors other than air pollution | |
Nine healthy young U.S. policemen | Physiologic measurements before and after 8-hr work shift; average in-vehicle PM , 24 μg/m | Significant increases of heart rate variability, ectopic beats, blood inflammatory and coagulation markers, and red blood cell volume; per 10-μg/m PM effect on C-reactive protein, +32%; neutrophils, +6%; von Willebrand factor, +12%; and ectopic beats, +20%. | ||
Twelve healthy young subjects | Physiologic measurements before and after 1-hr cycling trip from city center to university in Utrecht | Statistically nonsignificant 1–3% decrements in lung function per 10 /m soot concentration and a 15% increase in exhaled NO per 38,000 particles/cm |
Abbreviations: EC, elemental carbon; HP, Hyde Park; MI, myocardial infarction; NO, nitric oxide; OS, Oxford Street; RR, relative risk; UFP, ultrafine particle count.
Furthermore, there is a fairly substantial body of evidence of human controlled exposure studies in which volunteers have been exposed for 1–2 hr to diesel exhaust and to filtered air for comparison [see Supplemental Material, Table 1 (doi:10.1289/ehp.0901747)]. Typically, the evaluated exposures (100–300 μg/m 3 ) are higher than those encountered in ambient air, although not excessively. Because of ethical concerns, only physiologic effects have been studied with this study design. These studies have documented airway and systemic inflammation after exposure to diesel exhaust in patients and in healthy subjects.
Individual effects.
Because the physiologic changes observed in epidemiologic and controlled exposure studies likely play a role in the pathway to cardiac events of long-term exposure, it is plausible that these more adverse effects may occur in susceptible subjects. We calculated the potential impact on mortality of a transition from using a car to a bicycle for a 30-min (7.5-km) or 1-hr (15-km) commute based upon relative risk estimates from long-term exposure studies of mortality in association with PM 2.5 ( Pope et al. 2002 ) and black smoke (BS) ( Beelen et al. 2008 ).
The derivation of these risk estimates is provided in the Supplemental Material, Table 2 (doi:10.1289/ehp.0901747); Table 3 shows the results. We assumed that the actual risk related to long-term air pollution exposure is determined by the inhaled daily dose of PM 2.5 or BS. First, we calculated the inhaled pollution dose during commuting (car driving or cycling) and noncommuting hours based on prior information concerning minute ventilation rates (liters per minute) and PM 2.5 and BS exposures (micrograms per cubic meter) during sleep, rest, driving, or cycling. Next, we estimated the total daily dose for PM 2.5 and BS (micrograms per day) for driving or cycling. We then used the ratio of the total daily doses for the two travel modes to derive an “equivalent” change in PM 2.5 or BS concentration (micrograms per cubic meter) that could be normalized to the 10-μg/m 3 increase in long-term exposures used by Pope et al. (2002) and Beelen et al. (2008) to estimate the relative risk associated with the estimated change in long-term PM 2.5 and BS exposures that would result from a shift to commuting by bicycle instead of by car.
Potential mortality impact of cycling compared with car driving, for 0.5- and 1-hr commute, estimated for PM 2.5 and BS. a
Travel mode | Duration of travel (hr/day) | PM /BS concentration (μg/m ) | Inhaled dose (μg/day) | Total dose for car or bicycle (μg/day) | Equivalent change in PM or BS (μg/m ) | RR mortality, equal toxicity | RR mortality, traffic 5× more toxic |
---|---|---|---|---|---|---|---|
PM | |||||||
Car | 0.5 | 40.0 | 12.0 | 246 | |||
Cycle | 0.5 | 34.5 | 22.8 | 257 | 0.9 | 1.005 | 1.026 |
Car | 1.0 | 40.0 | 24.0 | 252 | |||
Cycle | 1.0 | 34.5 | 45.5 | 274 | 1.8 | 1.010 | 1.053 |
BS | |||||||
Car | 0.5 | 30.0 | 9.0 | 126 | |||
Cycle | 0.5 | 18.2 | 12.0 | 129 | 0.2 | 1.001 | 1.006 |
Car | 1.0 | 30.0 | 18.0 | 132 | |||
Cycle | 1.0 | 18.2 | 24.0 | 138 | 0.5 | 1.002 | 1.012 |
RR, relative risk.
Assuming equal toxicity of particles, the estimated relative risk associated with the change in PM 2.5 inhalation due to cycling instead of car driving ranges from 1.005 to 1.010. If we assume that traffic PM is more toxic than ambient PM 2.5 in general, these relative risk estimates range from 1.026 to 1.053. This assumption is supported by an analysis of PM from different sources, indicating the strongest associations with mortality from traffic particles ( Laden et al. 2000 ). If the assessment is based on BS, relative risk estimates are smaller (between 1.001 and 1.012).
The modal shift will reduce overall air pollution levels, which may result in health benefits of the general city population. An indication of the potential reduction in air pollution was obtained by using the Dutch dispersion model CAR (Calculation of Air pollution from Road traffic) ( Eerens et al. 1993 ). For a typical major urban street with a traffic intensity of 10,000 vehicles/day, for a 12.5% reduction in traffic intensity, concentration reductions were 1.3 μg/m 3 for nitrogen dioxide (NO 2 ) and 0.4 μg/m 3 for particles with aerodynamic diameter ≤ 10 μm (PM 10 ). The relative risk of long-term exposure to NO 2 expressed per 10-μg/m 3 increase on all-cause mortality is 1.10 ( Tonne et al. 2008 ). This implies that for the approximately 800,000–1,600,000 subjects living in major streets in the Netherlands, mortality rates could be 1.012 times lower. This relative risk is of the same order of magnitude as the estimated increased risk to the cyclist described in the previous section and applies to a larger population.
According to the WHO (2004) , road traffic injuries accounted for approximately 2% of all global deaths, making them the 11th leading cause of global deaths. The rates of road traffic death vary considerably among countries, transport mode, type of area (urban or rural), and person. Among several European countries, the highest fatality rates are about 3.5 times higher than the lowest figures [see Supplemental Material, Figure 1 (doi:10.1289/ehp.0901747)] ( International Transport Forum 2010 ).
Table 4 shows the estimated numbers of traffic deaths per age category per billion passenger kilometers traveled by bicycle and by car (driver and passenger) in the Netherlands for 2008 ( CBS 2008 ). These data suggest that there are about 5.5 times more traffic deaths per kilometer traveled by bicycle than by car for all ages, and that cycling is riskier than travel by car for all age groups except young adults (15–30 years of age), with about 9 times more deaths among those < 15 years of age, and 17 times more deaths among those > 80 years of age. The comparison in Table 4 probably overestimates the difference between cyclists and car drivers for short trips, because the relatively safe long car trips driven on highways are included. Across Europe, 8% of traffic deaths occur on the motorways, whereas 25% of the kilometers driven are on motorways ( European Road Transport Safety 2008 ). Risks for nonfatal accidents are higher for cyclists than for car drivers, as well [Supplemental Material, Table 3 (doi:10.1289/ehp.0901747)].
Traffic deaths per age category per billion passenger kilometers by bicycle and by car in the Netherlands. a
Age category (years) | Bicycle | Car | Ratio |
---|---|---|---|
< 15 | 4.9 | 0.6 | 8.6 |
15–20 | 5.4 | 7.4 | 0.7 |
20–30 | 4.2 | 4.6 | 0.9 |
30–40 | 3.9 | 2.0 | 2.0 |
40–50 | 6.6 | 1.0 | 6.9 |
50–60 | 9.6 | 1.2 | 7.9 |
60–70 | 18.6 | 1.6 | 11.7 |
70–80 | 117.6 | 7.6 | 15.4 |
> 80 | 139.6 | 8.1 | 17.1 |
Total average (all ages) | 12.2 | 2.2 | 5.5 |
Total average (20–70 years of age) | 8.2 | 1.9 | 4.3 |
Data from CBS (2008) .
For society, the risk that car drivers present to cyclists and pedestrians must also be taken into account. For the Netherlands, an analysis has compared the risks of a fatal accident for car drivers and cyclists, including the risk to other road users ( Dekoster and Schollaert 1999 ). The analysis excluded motorways, because cyclists cannot use these roads. Mortality rates were similar for car drivers and cyclists (20.8 vs. 21.0 deaths per million kilometers traveled). People older than 50 years are less frequently involved in fatal accidents when driving a car than when driving a bicycle, but the opposite is true for people 18–49 years of age [Supplemental Material, Table 4 (doi:10.1289/ehp.0901747)]. Jacobsen (2003) showed that in different European countries, the number of traffic deaths of cyclists is inversely related to the amount of cycling [Supplemental Material, Figure 2 (doi:10.1289/ehp.0901747)], suggesting a “safety-in-numbers” effect.
For 18- to 64-year-old individuals, the risk of a fatal accident while cycling is about 4.3 times higher compared with the same distance by car ( Table 4 ). The fatal traffic accident rate for cyclists 20–70 years of age is about 8.2 deaths per billion passenger kilometers traveled, whereas the risk for car drivers and passengers the rate is 1.9 deaths per billion passenger kilometers traveled ( Table 4 ). A population of 500,000 commuting 7.5 km/day will commute 1.36785 billion km/year (7.5 km/day × 365 days/year × 500,000). From the data shown in Table 4 , we estimate that this amount of car travel would result in approximately 2.6 deaths/year (1.9 × 1.36785). An equivalent amount of bicycle travel would result in approximately 11.2 deaths/year (8.2 × 1.36785). In the Netherlands, the all-cause mortality rate for 18- to 64-year-old persons is 235.1 per 100,000 per year ( CBS 2008 ) or 1,176 persons per 500,000 per year. Hence, among 18- to 64-year-olds, the relative risk of all-cause mortality associated with a 7.5 km/day shift from driving to cycling would be [1,176 + (11.2 – 2.6)]/1,176 = 1.007. When we use age-specific data, relative risks ranged from 0.996 to 1.010. For the 15-km scenario, age specific relative risks ranged from 0.993 to 1.020.
The societal impact of a modal switch on the number of fatal accidents largely depends on which people switch from car to bicycle. If it is the average population, the impact (including risk presented to other road users) would be practically zero [Supplemental Material, Table 4 (doi:10.1289/ehp.0901747)], but if young car drivers switched to a bicycle, it would decrease the number of fatal accidents. The opposite is true for elderly car drivers.
Levels of inactivity are high in virtually all developed and developing countries.a The WHO (2007a) estimates that 60–80% of the world’s population does not meet the recommendations required to induce health benefits. For Europe 62.4% inactive adults are estimated ranging from 43.3% (Sweden) to 87.7% (Portugal) ( Varo et al. 2003 ). In the Netherlands about 62% of the population is sedentary ( Varo et al. 2003 ). The WHO estimates that the prevalence of physical inactivity accounts for 22% of cardiovascular disease prevalence globally ( WHO 2007a ). There is sufficient evidence for an association between physical activity and mortality, cardiovascular disease (hypertension), diabetes, obesity, cancer (colon and breast), osteoporosis, and depression ( Bauman 2004 ; Warburton et al. 2006 ). Because only a few studies specifically reported on the beneficial health effects of cycling, we also summarized the quantitative evidence of beneficial health effects of physical activity, making use of review papers.
Recently, the American College of Sports Medicine and the American Heart Association published an updated recommendation for physical activity ( Haskell et al. 2007 ). To promote and maintain health, all healthy adults 18–65 years of age need moderate-intensity aerobic physical activity for a minimum of 30 min on 5 days each week or vigorous-intensity aerobic activity for a minimum of 20 min on 3 days each week. Also, combinations of moderate- and vigorous-intensity activity can be performed to meet this recommendation. For young people, 60 min of moderate to vigorous physical activity on a daily basis is recommended ( Strong et al. 2005 ). In several physical activity studies, metabolic equivalent of task (MET) is used as an indicator of physical activity, and the minimum goal should be in the range of 500–1,000 MET min/week. Leisure cycling or cycling to work (15 km/hr) has a MET value of 4 and is characterized as a moderate activity ( Ainsworth et al. 2000 ). Hence, a person shifting from car to bicycle for a daily short distance of 7.5 km would meet the minimum recommendation (7.5 km at 15 km/hr = 30 min) for physical activity in 5 days (4 MET × 30 min × 5 days = 600 MET min/week).
Table 5 provides summary estimates from reviews for the impact of physical activity on all-cause mortality, and includes only estimates that are relevant to compare the risks for cyclists and car drivers. It is difficult to synthesize information across studies because investigators have measured physical activity in different ways and classified physical activity according to different dose schemes that often are difficult to compare directly ( Lee and Skerrett 2001 ). Several reviews have suggested that the relative risk of mortality for those who meet the recommended levels of physical activity compared with the inactive group is between 0.65 and 0.80 ( Bauman 2004 ; Lee and Skerrett 2001 ; Warburton et al. 2006 ).
Potential impact of physical activity on all-cause mortality in various reviews a and cohort studies.
Source | Definition of physical activity | Relative risk | Comments |
---|---|---|---|
Reviews | |||
Meeting moderate physical activity recommendation (1,000 kcal/week) | 0.70–0.80 | Review, excluding papers examining only two levels of physical activity | |
Expending of 1,000 kcal/week | 0.70 | Based on a symposium; invited experts reviewed the existing literature | |
Meeting physical activity recommendation | 0.70 | Review of peer-reviewed studies published between 2000 and 2003 | |
Different definitions of physical activity | 0.70–0.87 (moderate) 0.46–0.92 (vigorous) | Review | |
Meeting physical activity recommendation | 0.65–0.80 | Review | |
Different definitions including moderate exercise (4,100–7,908 kJ/week), vigorous exercise, and different distances walked | 0.50–0.77 | Review of adult cohort studies with a mean > 60 years of age | |
Studies on cycling | |||
Cycling to work for 3 hr/week | 0.55–0.72 | Based on a Danish cohort, adjusted for leisure time physical activity (among others) | |
Walking and cycling to work | 0.71–0.79 | Based on a Finnish cohort study among subjects with type 2 diabetes; estimates without adjusting for other domains in physical activity | |
Cycling to work (MET-hours/day) | 0.66–0.79 | Based on a Chinese women cohort in Shanghai, adjusted for other physical activity | |
Overall summary | 0.50–0.90 |
Three studies have directly assessed mortality related to cycling to work. In a prospective study in Copenhagen, the relative risk of the group bicycling to work was 0.72 [95% confidence interval (CI), 0.57–0.91] compared with other modes of transport after multivariate adjustment, including leisure-time physical activity ( Andersen et al. 2000 ). The relative risk for physically active groups compared with the sedentary group decreased with activity level: 0.68, 0.61, and 0.53 ( Andersen et al. 2000 ). In the Shanghai Women’s Health Study, exercise and cycling for transportation were both inversely and independently associated with all-cause mortality ( Matthews et al. 2007 ). Hazard ratios were 0.79 (95% CI, 0.61–1.01) for the group cycling 0.1–3.4 metabolic equivalent hours per day and 0.66 (95% CI, 0.40–1.07) for the group cycling > 3.4 metabolic equivalent hours per day, compared with the noncycling group. A Finnish study that combined cycling and walking to work versus nonactive commuting also showed significantly lower relative risks for active commuters in the range of 0.71 and 0.79 ( Hu et al. 2004 ). According to the reviews and the three cycling studies, the relative risk for all-cause mortality is in the range of 0.50–0.90 ( Table 5 ).
An expert panel determined a generally linear relationship between physical activity level and the rates of all-cause mortality, total cardiovascular disease, and coronary heart disease incidence and mortality ( Kesaniemi et al. 2001 ). There is thus evidence that health gains occur for physically active and nonactive persons, although the magnitude of these benefits may differ.
To calculate the potential impact of the modal shift on mortality, we directly used the range of relative risk estimates (0.50–0.90) presented in Table 5 .
For the people who shift from car to bicycle use for short trips, we estimated that the beneficial effect on all-cause mortality rates of the increased physical activity due to cycling is substantially larger (relative risk, 0.50–0.90) than the potential mortality effect of increased inhaled air pollution doses (relative risk, 1.001–1.053) and the effect on traffic accidents (age-specific relative risk, 0.993–1.020). The estimated gain in life expectancy per person from an increase in physical activity ranged from 3 to 14 months ( Table 6 ). The estimated life expectancy lost because of air pollution (0.8–40 days) and traffic accidents (5–9 days) was much smaller. On average, the benefits of cycling were about 9 times larger than the risks of cycling, compared with car driving for the individuals making the shift, calculated as 337,896/(28,135 + 9,639). The estimated number of life years gained still exceeded the losses when the lowest estimate for physical activity was compared with the highest estimate for air pollution and traffic accidents (benefits/risks ratio of 2).
Summary of impact on all-cause mortality for subjects shifting from car to bicycle.
Stressor | Relative risk | Gain in life years | Gain in life days/months per person |
---|---|---|---|
Air pollution | 1.001 to 1.053 | −1,106 to −55,163 (−28,135) | −0.8 to −40 days (−21 days) |
Traffic accidents | 0.996 to 1.010 0.993 to 1.020 | −6,422 to −12,856 (−9,639) | −5 to −9 days (−7 days) |
Physical activity | 0.500 to 0.900 | 564,764 to 111,027 (337,896) | 14 to 3 months (8 months) |
The largest estimated gain in life years was for the elderly [Supplemental Material, Table 6 (doi:10.1289/ehp.0901747)]. The ratio of life years gained to lost was 8.4 for persons < 40 years of age, 8.6 for persons 40–64 years of age, and 10.8 for persons ≥ 65 years of age.
The relative benefits of a 7.5-km versus 15-km distance are probably similar. A 15-km distance (1-hr commute) increases the life-years lost for air pollution from 20 to 40 days based on PM 2.5 and increases the life-years lost for traffic accidents from 5 to 9 days. The total estimated number of days lost per person is thus 49 for a 15-km distance and 25 for a 7.5-km distance. The relative risk of physical activity is difficult to quantify with the approach employed here. Using the data from Matthews et al. (2007) , the relative risk would be 0.79 for the 7.5-km distance and 0.66 for the 15-km distance, assuming 4 MET associated with cycling. These relative risks translate in 280 and 173 days gained, respectively.
Principal findings.
We quantitatively compared the health benefits from physical activity with the risks related to air pollution and traffic accidents between cycling and car driving for short trips, distinguishing the individuals who shift modes of travel from society as a whole. Estimated inhaled air pollution doses were higher in cyclists. The risk of a fatal traffic accident is higher for cyclists than for car drivers. Substantial benefits of physical activity have been demonstrated, including decreased cardiovascular disease and mortality.
For the people who shift from car to bicycle, we estimated that the well-documented beneficial effect of increased physical activity due to cycling resulted in about 9 times more gains in life-years than the losses in life years due to increased inhaled air pollution doses and traffic accidents. For the society as a whole this can be even larger because of reduced air pollution emissions. If the risk presented to other road users is included, the risk of a fatal traffic accident is virtually the same for cyclists and car drivers.
The strength of our assessment is especially the quantitative comparison of benefits and risks, in a common scenario for the three stressors evaluated. It could be argued that the Copenhagen ( Andersen et al. 2000 ) and Chinese studies ( Matthews et al. 2007 ) of the effects of bicycling on mortality have already demonstrated the net effect of physical activity on all-cause mortality, including the negative effects of fatal traffic accidents and air pollution. However, the size of the potential negative health effects was not quantified separately in those studies. Therefore it is difficult to transfer the net effect of these studies to other locations, where traffic accident rates and air pollution may be different. Because in our assessment the separate risks have been disentangled, it is possible to make assessments for different settings, by using other input data (e.g., traffic mortality rates).
We performed our calculations for the Netherlands, where an extensive cycling infrastructure exists and priority is given to cyclists over other traffic—factors that contribute to regular cycling. Restrictions to car use through traffic calming in residential areas and car-free zones influence cycling behavior as well ( Pucher and Dijkstra 2003 ). Apart from the highest average distance cycled per person, the Netherlands is also one of the safest countries in terms of fatal traffic accidents. In such countries as the United Kingdom, Spain, and France, the risk of a fatal traffic accident for cyclists is substantially higher, probably also relative to car driving [Supplemental Material, Figure 2 (doi:10.1289/ehp.0901747)]. When we repeated the traffic accident calculations for the United Kingdom, where the risk of dying per 100 million km for a cyclist is about 2.5 times higher [Supplemental Material, Figure 2 (doi:10.1289/ehp.0901747)] and assuming the same fatality risk for car drivers as in the Netherlands, resulting life expectancy losses were approximately 14 days/person, based on 2005 population data from the United Kingdom and Wales. Overall, benefits of cycling are still 7 times larger than the risks.
Calculations on mortality impacts were performed for people 18–64 years of age, because people in that age range are more likely to make the modal shift. Age-specific analysis showed that the relative benefits of cycling are highest in the older age categories. This may have been even more pronounced if we had taken into account that the relative risks of physical activity may be larger for the elderly ( Vogel et al. 2009 ). The empirical evidence for higher relative risks in elderly related to long-term exposure to air pollution is weak; for example, in the large American Cancer Society study there were no differences in relative risk for PM 2.5 ( Pope et al. 2002 ). We did not include children in our assessment because they are unable to drive a car, so a modal shift is not possible. Because of our focus on mortality effects (being extremely rare in children), we could not quantitatively compare risks for children as car passengers or as cyclists for physical activity and air pollution. The benefits of physical activity in children are considered important, however, both for current and for future health.
Overall relative risks may largely reflect the response from sensitive subgroups. For all stressors, the elderly are likely more susceptible, and we documented in an additional analysis that the ratio of benefits and risks was highest for ≥ 65-year-olds. For air pollution, subjects with preexisting cardiorespiratory disease may be more susceptible, and for physical activity, sedentary people may be more susceptible; these are subgroups that may partly overlap. Hence, both the risks and benefits may be higher than in the population average analysis.
In summary, it is unlikely that the conclusion of substantially larger benefits from cycling than risks is strongly affected by the assumptions made in the scenario, including the use of data from the Netherlands. Because concentration–response functions are mostly based on studies in Europe and North America, they may not apply in developing countries. For air pollution, there are no studies on long-term mortality effects in developing countries. The generally higher ambient air pollution concentrations could lead to higher losses in life-years comparing cycling and car driving. Traffic accident statistics for the Netherlands are probably not transferable to developing countries. For physical activity, there is evidence from a Chinese study ( Matthews et al. 2007 ), with very similar benefits. Hence, very large differences in concentration–response functions for air pollution and traffic accidents from the functions we used would be necessary to tip the balance between benefits and risks.
For air pollution, there is considerable evidence that long-term and short-term exposures are related to increased cardiopulmonary mortality ( Brunekreef and Holgate 2002 ). There are no studies of mortality effects specifically related to in-traffic exposures. We estimated the effect of shifting mode using two major long-term mortality cohort studies ( Beelen et al. 2008 ; Pope et al. 2002 ), making assumptions about the contribution of traffic participation to the total inhaled dose of PM 2.5 and (diesel) soot. Relative risks comparing cycling and car driving were small for both approaches, with the lower estimates based upon BS probably most realistic, because this component is more specific for traffic emissions.
The actual risk may be smaller because cyclists could more easily choose a low-traffic route. The substantial influence of route has been documented in various monitoring and modeling studies ( Adams et al. 2001 ; Hertel et al. 2008 ; Kingham et al. 1998 ; Strak et al. 2010 ). A study in Utrecht found 59% higher UFP exposure for cyclists along a high-traffic route compared with a low-traffic route ( Strak et al. 2010 ). Walking close to the curb in London greatly increased personal exposures ( Kaur et al. 2005 ). For cyclists, position on the road is likely important as well, because it determines distance to motorized traffic emissions. Urban planning may also contribute by separating cycle lanes from heavily trafficked roads ( Thai et al. 2008 ).
For society, reduced overall air pollution levels may result in lower mortality from long-term exposure of city dwellers. The potential benefits we estimated based on NO 2 reductions were in the same order of magnitude as the potential risks for the individuals shifting.
Table 4 shows that the modal shift will lead to an increase in traffic accident deaths. The relative risk may be lower than we used because of the “safety-in-numbers” effect [Supplemental Material, Figure 2 (doi:10.1289/ehp.0901747)]. Car drivers may take more account of cyclists, resulting in fewer accidents per car-kilometer, when cyclists form a bigger part of the traffic ( Jacobsen 2003 ). Traffic fatality and injury rates in Germany and the Netherlands (with relatively high levels of cycling and walking) were relatively low compared with those of the United States ( Pucher and Dijkstra 2003 ). However, whether this reduction is attributable to a safety-in-numbers effect or a result of more biking lanes cannot easily be disentangled. The WHO concluded that if promotion of active commuting is accompanied by suitable transport planning and safety measures, active commuters are likely to benefit from the safety-in-numbers effect ( WHO 2007b ). The relative risks could also be higher because the less experienced cyclists making the shift could be more vulnerable to accidents. We cannot quantify this effect.
Even when origin and destination are the same, cars and bicycles often take different routes ( Witlox 2007 ). The same short trip for a car may be 20–50% longer than for a bicycle (our calculations are based on comparisons per kilometer). If we could make a trip-based comparison, a lower relative risk for fatal accidents for cyclists compared with car drivers would be found. Furthermore, we did not take into account the concept of constant travel time budgets ( van Wee et al. 2006 ): A change of travel time will be compensated by a change of destination. When taking the bicycle, the shop next door is preferred over the shop with greater choices farther away. These factors would lead to lower relative risks than we used.
Relative risks for different physical activity definitions (total physical activity, meeting the physical activity guideline, active commuting) were quite consistent. An important issue is whether the comparison between subjects with lower and higher physical activity can be used to assess the health effects of a change in physical activity related to a shift toward active commuting. Bauman (2004) showed that persons who were already in the highest quartile of fitness at baseline had a significantly lower mortality when they became even more active. In another study, people who went from unfit to fit over a 5-year period had 44% relative risk reduction compared with people who remained unfit ( Blair et al. 1995 ). The largest improvements in health status are seen in inactive persons who change their lifestyle and become physically active ( Warburton et al. 2006 ). A review by Erikssen et al. (1998) suggested similar health benefits from an increase in physical activity for active and sedentary persons. Already active persons could have lower benefits of the extra physical activity, leading to relative risks up to 0.90. If only active persons shift mode of transport, lower overall benefits of cycling compared with car driving will be found (ratio of life-years gained vs. lost, 4 instead of 9).
An increase in cycling does not necessarily lead to an increase in total physical activity, if it is associated with reduced activity in another domain ( Forsyth et al. 2008 ; Thomson et al. 2008 ). The empirical evidence for substitution is weak, and increased fitness could also lead to more physical activity in leisure time. If we assume that for 25% of the population no health gains occur because of substitution, the ratio of benefits to risks (central estimates from Table 6 ) would be reduced from 8.9 to 6.7. Only if for 89% of the population no increase in total physical activity occurs because of substitution would benefits and risk become equal.
We have not considered the negative effects of physical activity on health—namely, musculoskeletal injury and fatal and nonfatal cardiac events ( Institute of Medicine 2007 ). Cycling can be considered a moderate type and duration of sport and has lower injury risk than do more vigorous types (running, scholastic athletics) and longer durations of physical activity ( Hootman et al. 2001 ; Parkkari et al. 2004 ). Exercise has acute cardiac risks as well, but the absolute risk of a cardiac event during exercise seems to be low ( Institute of Medicine 2007 ). Regular physical activity also reduces the acute risk of a cardiovascular event ( Tofler and Muller 2006 ).
We limited the quantitative assessment to mortality. It is difficult to evaluate the comparison between cycling and car driving if morbidity is included because of the lack of solid concentration–response relationships for air pollution and physical activity for morbidity outcomes. A meta-analysis reported a consistent positive association between physical activity and health-related quality of life ( Bize et al. 2007 ). The largest cross-sectional study showed that people meeting the recommended levels of physical activity had an adjusted odds ratio of “having 14 or more unhealthy days during the previous months” of 0.4 (95% CI, 0.36–0.45) over the inactive subjects ( Bize et al. 2007 ). Quality of life may even further improve apart from the increases in life-years. Concentration–response functions for air pollutants and morbidity outcomes such as hospital admissions are lower than for mortality: in the range of 1% compared with 6% per 10-μg/m 3 increase in PM 2.5 ( WHO 2006 ). Traffic injuries may differ even more between cyclists and car drivers than fatal accidents [Supplemental Material, Table 4 (doi:10.1289/ehp.0901747)], if underreporting of especially cyclist accidents is accounted for. This would reduce the ratio between benefits and risks.
We did not include all stressors in the quantitative evaluation. Cycling contributes to other benefits, including reduced emissions of carbon dioxide relevant for reducing climate change, reduced use of physical space (e.g., related to parking), and reduced traffic noise for city dwellers, which may result in less annoyance. We are not aware of exposure studies or health effects studies that have compared traffic noise during transport for cyclists and car drivers.
Our study suggests that policies stimulating cycling likely have net beneficial effects on public health. Policies should be accompanied by safety measures and efforts to limit hazards, for example, by infrastructural choices (building cycling lanes away from major roads to limit cyclists’ air pollution exposures) or limitations such as a ban on car traffic during school start and end hours near schools. Policies may take the age dependence of the traffic accident relative risks into account—for example, by stimulating especially the young to increase cycling. However, this may not be the optimal choice for the beneficial effects of cycling.
Assessing what traffic policies are effective in promoting a population shift from using cars toward cycling (and walking) is beyond the scope of this review. A recent review showed that targeted behavior change programs can change the behavior of motivated subgroups, resulting in a 5% shift of all trips at the population level in the largest study ( Ogilvie et al. 2004 ). However, effects of similar programs on the general, less motivated population are unclear. Those programs may benefit from taking the public’s views into account and learning from good practices (e.g., THE PEP 2009 ). In particular, perceptions of walking and cycling as dangerous activities are an important barrier to the promotion of active transport ( Lorenc et al. 2008 ).
On average, the estimated health benefits of cycling were substantially larger than the risks of cycling relative to car driving. For the society as a whole, this can be even larger because there will be a reduction in air pollution emissions and eventually fewer traffic accidents. Policies stimulating cycling are likely to have net beneficial effects on public health, especially if accompanied by suitable transport planning and safety measures.
This research was conducted within the framework of INTARESE (Integrated Assessment of Environmental Stressors in Europe), funded by European Union 6th Framework Programme grant 018385-2.
Supplemental Material is available online (doi:10.1289/ehp.0901747 via http://dx.doi.org/ ).
Greater Good Science Center • Magazine • In Action • In Education
All humans strive to be happy in some form. While there are intriguing variations in what exactly it means to be happy , this tenet is one of the rare human universals, transcending differences in culture, geographic location, age, ethnicity, and gender. As the Dalai Lama put it , simply, “The purpose of life is to be happy.”
That might lead to the expectation that we should all be happy, at least when circumstances afford it. Yet this is not the case. Even when people’s lives are good, many feel less than happy, and may be beset by anxiety and depression.
Thus there is a paradox: The pursuit of happiness is one of the prime values people hold, and they often fall short of attaining it. There might even be a further vexing twist on this happiness paradox, by which the more fervently people pursue happiness the further they get from it. In the words of the philosopher Eric Hoffer, “The search for happiness is one of the chief sources of unhappiness.”
The idea is that the more we value happiness the higher expectations we set for our happiness—high expectations we are more likely to miss. When we miss them, we may become disappointed and discontented. Such feelings are incompatible with happiness. And voila! Like in quicksand, the more we want to be happy, the less happy we become.
Fortunately, our research points to a solution—and the solution is pretty simple to state, if tricky to implement: When you’re experiencing something positive, don’t judge yourself.
In earlier empirical research , we showed that intensely valuing happiness indeed seems to backfire. For example, people who endorsed statements like, “Happiness is extremely important to me,” were more likely to have lower well-being and greater depressive symptoms.
Intriguingly, this was especially the case when the circumstances of people’s lives were good. This is in line with the idea that the happiness paradox trap becomes engaged when expectations for happiness are activated—when we think everything is good and we ought to feel happy.
A recent New York Times opinion piece elaborates on the ways in which this happens, and puts its finger on one particular aspect of pursuing happiness that might interfere with attaining it: tracking it. It asked: “Could tracking happiness make us feel worse?” The answer to the question finds a resounding yes, it could and it does.
Tracking happiness may interfere with attaining happiness for two key reasons. First, when we track our happiness we are pulled out of the moment, which interferes with experiencing happiness to its fullest. This follows a suspicion memorably voiced by John Stuart Mill: “Ask yourself whether you are happy and you cease to be so.”
The second reason why tracking happiness might be harmful is that it invites comparison. And comparison—to our own high expectations, to other people’s blissful Instagram feeds—breeds discontent. This leads the happiness hunter directly into the place they wanted to avoid.
At this point, we might conclude that we should let go of our lofty goals to become happier. Maybe it is not in the cards for us and we should let go of the goal, and make do with whatever happiness scraps fall to us. But this conclusion does not accord with a large body of research that examines whether and how people can become happier.
Take, for example, UC Riverside psychologist Sonya Lyubomirsky’s research , which has found that Undermine Well-Being">happiness interventions can work in helping people be happier , at least sometimes. Meaning, when people want to feel happier, they can get there. The mystery is further deepened in that Lyubomirsky and her colleagues found this is especially true for people who are highly motivated and put forth more effort, as evidenced by selecting to be part of a happiness-enhancing intervention (compared to cognitive exercises).
Thus, there is a puzzle: How can valuing happiness be bad and pursuing happiness be good?
That puzzle led us to believe that the story must be more complicated. Perhaps valuing happiness—even intensely—is not inherently and always problematic. Rather, the problem might lie in how people approach happiness. There might be some bad and some good ways. That is, whether or not valuing happiness is associated with bad outcomes depends on the way in which people approach and think about happiness.
What might those ways be? UC Berkeley psychology alumni Felicia Zerwas and Brett Ford proposed a model of pursuing happiness that provides cues by taking a closer look at what happens psychologically when people pursue happiness. They proposed that it is OK to aspire to happiness, even intensely.
Where things start to get dicey is a bit further down the path where there is a fork in the road: On one path, someone can simply be OK with the level of happiness they have reached. But on the other path, someone can judge their experiences and worry about how much happiness they do or don’t have.
Going down this second path infuses negativity into their experiences, ultimately leading them further away from happiness. We can call this tendency concern about happiness. Concern about happiness, rather than simply aspiring to happiness, might lie at the heart of self-defeat.
What does it take to live a happier life? Learn research-tested strategies that you can put into practice today. Hosted by award-winning psychologist Dacher Keltner. Co-produced by PRX and UC Berkeley’s Greater Good Science Center.
Because this is a bit abstract, let us illustrate the two approaches with an example. Let’s say you are at a birthday party—your own! Your friends planned it for you and invited all your favorite people, who brought your favorite foods, treats, and beverages. You feel lots of positive emotion—contentment, excitement, gratitude, joy, and happiness. So far so good.
Now comes the key moment for our happiness hunter, where the path forks. On the one hand, you could simply aspire to being happy. Period. You enjoy the moment and dance the night away at your birthday party. End of story. On the other hand, however, you could be concerned about your happiness, adding judgment to your experience and with it a layer of overthinking. You have everything that should make you happy, and yet you wonder, you worry, This is perfect, why aren’t I happier? A disappointment sets in which might spiral into further disappointment.
Scientists call these “negative meta-emotions”: feelings we have about feelings. And so even when happiness is most within reach—or perhaps precisely because it is within reach—you get in your own way.
Now add to this the fact that few experiences are purely and unadulteratedly happy. Most events—even the best—have elements of ambiguity and mixed emotion. The cake might not be perfect or one of the guests might misbehave. We can easily see how the person who is concerned about happiness will latch on to those flies in the ointment and let them spoil the entire experience.
So to recap, when people who aspire to happiness have positive events, they can simply roll with it and enjoy their experiences. Even if there IS a fly in the ointment, that’s OK. In contrast, when people who are concerned about happiness have positive events, they cannot simply enjoy them. They yuck their own yum: They judge and add negative meta-emotions.
That all means that the problem may not lie in how happy people are or how happy they want to be—it lies in how people respond to their happiness.
We put these ideas to an empirical test in a but Not Aspiring to Happiness Is Linked With Negative Meta-Emotions and Worse Well-Being">recent series of studies involving 1,815 participants from across the U.S. We found that, indeed, people fall into two types, with some scoring high on aspiring to happiness, and some scoring high on concern about happiness.
In our survey, they endorsed statements like, “I am concerned about my happiness even when I feel happy,” and, “If I don’t feel happy, maybe there is something wrong with me.” People who were more concerned about their happiness experienced lower satisfaction with their lives, lower psychological well-being, and higher depression symptoms.
And, based on diary entries they completed, we found that this link was explained by how they responded to positive events: they were more likely to have negative meta-emotions like disappointment about their own feelings. It’s like a slow drip of weak poison, where every single experience doesn’t harm overall well-being, but repeated instances over many months do.
Meanwhile, aspiring to happiness—considering happiness very important but without a tendency to judge—was innocuous and did not interfere with attaining happiness.
What does our research teach us about whether the pursuit of happiness is possible? We believe the studies point to a solution to the happiness paradox. From the concerned people, we can learn which pitfalls to avoid , and from the aspirers we can learn how to make happiness attainable. Four of these lessons are supported by science:
This is not to say the only paths toward happiness are psychological. Our cultures, systems, and societies play a key role in individual happiness . First, they directly create happiness. For example, giving people money , supporting social connection, and combating inequality and injustice are some of the best ways to make people happier. Second, they shape how people approach happiness . For example, we learn from our culture how to think about happiness and how to go about pursuing it, whether we simply aspire or are concerned.
Happiness is a—maybe THE—core value throughout human history and across cultures. While there are pitfalls, attaining greater happiness is possible.
Iris Mauss, Ph.D. , is the Thomas and Ruth Ann Hornaday Professor of Psychology and the director of the Institute of Personality and Social Research at the University of California, Berkeley. Her lab’s research focuses on emotions and emotion regulation, with an emphasis on their links to psychological health.
Brett Q. Ford, Ph.D. , is an associate professor of psychology at the University of Toronto, where she directs the Affective Science and Health Laboratory. Her research examines how people manage emotions and cope with stress, exploring both the benefits and the costs of striving to feel good.
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The economic benefits and costs of cycling to wider society. There is a growing body of evidence indicating a net benefit to society of increasing participation in cycling as summarized in the following sections relating to cycling impacts on health, pollution and congestion, duty and taxation and employment and retail. 5.3.1.
The total sample size of the studies was 372 (306 women). Results revealed that indoor cycling may improve aerobic capacity, blood pressure, lipid profile, and body composition. These enhancements may be achieved as standalone intervention or combined with other physical exercises or diet. Conclusions: The combination of indoor cycling and diet ...
Active transportation, which is any form of human-powered transportation, can mitigate the health effects of the climate crisis while simultaneously improving the health of people. Physical activity improves overall well-being, as well as physical and mental health. Active transportation, particularly cycling, is a convenient way to meet ...
Improves strength and flexibility. Like other aerobic exercises, cycling can build up your muscular strength and endurance. According to Dr. Kubiak, research has shown that indoor cycling helps ...
Health aspects of day-to-day cycling have gained attention from the health sector aiming to increase levels of physical activity, and from the transport and planning sector, to justify investments in cycling. We review and discuss the main pathways between cycling and health under two perspectives — generalizable epidemiological evidence for ...
Cycling and walking can help fight overweight and reduce physical inactivity, which causes one million deaths per year in the European Region. Both means of active transport can also help to reduce air pollution that claims more than half a million deaths every year. Evidence shows that investments in policies that promote safe cycling and walking can play a crucial role in shaping health ...
Active transportation, which is any form of human-powered transportation, can mitigate the health effects of the climate crisis while simultaneously improving the health of people. Physical activity improves overall well-being, as well as physical and mental health. Active transportation, particularly cycling, is a convenient way to meet ...
The purpose of this study was to update the evidence on the health benefits of cycling. A systematic review of the literature resulted in 16 cycling-specific studies. Cross-sectional and longitudinal studies showed a clear positive relationship between cycling and cardiorespiratory fitness in youths.
Humans. Male. Middle Aged. Physical Fitness. The purpose of this study was to update the evidence on the health benefits of cycling. A systematic review of the literature resulted in 16 cycling-specific studies. Cross-sectional and longitudinal studies showed a clear positive relationship between cycling and cardiorespiratory fitness in youths ….
Research that addresses cycling and explores it in the context of public gains has found its benefits to include cost savings, savings on journey time, convenience, health, and perceived utility ...
5. Cycling boosts mental health and brain power. Cycling can ease feelings of stress, depression, or anxiety. Focusing on the road or your cadence when cycling can help you develop concentration ...
11. Less Stress. Everyone knows that exercise can help reduce stress, but a 2018 study in the Lancet of over one million (!) participants confirmed that cycling is one of the top stress-busting ...
According to Walker, "Research suggests that physical activity like cycling likely encourages new cell growth in areas of the brain linked to memory and problem solving, and can support stronger ...
Bicycling. Bicycling, also referred to as biking or cycling, is a form of transportation and a popular leisure-time physical activity. Health benefits include improved cardiovascular fitness, stronger muscles, greater coordination and general mobility, and reduced body fat. As with other types of exercise, it can also help improve mental health ...
The top 5 benefits of cycling. August 11, 2016. Going for a ride is good for your heart and muscles, and it may improve how you walk, balance, and climb stairs. Image: DTStockPhotos. They say you never forget how to ride a bike, so maybe it's time to climb aboard a two- or three-wheeler and enjoy the health benefits of cycling.
Given the associations between cognitive function, well-being and exercise in older adults, the aim of the study reported in this paper was to investigate the effect of cycling outdoors on cognitive function and mental health and well-being of older adults (over 50 years old). Compared to other studies, which measure effect of indoor exercise ...
Background Encouraging cycling is an important way to increase physical activity in the community. The Cycling Connecting Communities (CCC) Project is a community-based cycling promotion program that included a range of community engagement and social marketing activities, such as organised bike rides and events, cycling skills courses, the distribution of cycling maps of the area and coverage ...
Cycling relieves stress. Chronic stress can have big health impacts. But physical activities like cycling can help reduce daily stress. "Any time you exercise, it releases endorphins," says Thoman. Endorphins can help you feel better when you are under stress. And, exercising outdoors has added benefits.
Study shows how a pedal-powered commute can set you up for the whole day. Cycling can help reduce stress and improve your work performance, new research confirms. New research from Concordia's ...
Being a powerful rider can help you flip the switch between simply enduring a ride to actually enjoying a ride. ... Aside from how muscle power can help your cycling, research has also found that ...
For riders who aren't coached, enlisting a strategy of two or three weeks of structured training with a week of easier-intensity riding can help balance things. Another great method to prevent ...
In addition, cycling can help to protect the environment and reduce greenhouse gas emissions. The primary aim of this scoping review is to identify the currently available scientific evidence and gaps of research in this field. ... However, it seems to be highly relevant to conduct more research on cycling among older adults in low- and middle ...
VeloSano 'Bike to Cure' event returns to Cleveland: How you can help raise money for cancer research. 100% of the money VeloSano raises is used to benefit cancer research at the Cleveland Clinic.
Breast radiologists at Kaiser Permanente will research how an artificial intelligence tool may help detect breast cancers at earlier stages, before cancers can be seen by the human eye, and when it is most responsive to treatment. ... Radiologists to Research How AI Can Help Detect Breast Cancer September 4, 2024 . Kaiser Permanente Mid ...
A Finnish study that combined cycling and walking to work versus nonactive commuting also showed significantly lower relative risks for active commuters in the range of 0.71 and 0.79 (Hu et al. 2004). According to the reviews and the three cycling studies, the relative risk for all-cause mortality is in the range of 0.50-0.90 (Table 5).
Acceptance can help us become happier and enjoy life more, and it also is a helpful strategy to be resilient when we encounter adversity. Next, consider counteracting one of the main tributaries to judgment: monitoring how we feel. Monitoring itself is not harmful but it makes it a lot more likely that we will judge.