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Financial Incentives to Promote Active Travel

An Evidence Review and Economic Framework
  • Adam Martin
    Correspondence
    Address correspondence to: Adam Martin, MSc, Health Economics Group, Norwich Medical School, University of East Anglia, Norwich, United Kingdom NR4 7TJ
    Affiliations
    Health Economics Group, Norwich Medical School, University of East Anglia, Norwich, United Kingdom

    UKCRC Centre for Diet and Activity Research, Institute of Public Health, Cambridge, United Kingdom
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  • Marc Suhrcke
    Affiliations
    Health Economics Group, Norwich Medical School, University of East Anglia, Norwich, United Kingdom

    UKCRC Centre for Diet and Activity Research, Institute of Public Health, Cambridge, United Kingdom
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  • David Ogilvie
    Affiliations
    MRC Epidemiology Unit, Cambridge, United Kingdom

    UKCRC Centre for Diet and Activity Research, Institute of Public Health, Cambridge, United Kingdom
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      Context

      Financial incentives, including taxes and subsidies, can be used to encourage behavior change. They are common in transport policy for tackling externalities associated with use of motor vehicles, and in public health for influencing alcohol consumption and smoking behaviors. Financial incentives also offer policymakers a compromise between “nudging,” which may be insufficient for changing habitual behavior, and regulations that restrict individual choice.

      Evidence acquisition

      The literature review identified studies published between January 1997 and January 2012 of financial incentives relating to any mode of travel in which the impact on active travel, physical activity, or obesity levels was reported. It encompassed macroenvironmental schemes, such as gasoline taxes, and microenvironmental schemes, such as employer-subsidized bicycles. Five relevant reviews and 20 primary studies (of which nine were not included in the reviews) were identified.

      Evidence synthesis

      The results show that more-robust evidence is required if policymakers are to maximize the health impact of fiscal policy relating to transport schemes of this kind.

      Conclusions

      Drawing on a literature review and insights from the SLOTH (sleep, leisure, occupation, transportation, and home-based activities) time-budget model, this paper argues that financial incentives may have a larger role in promoting walking and cycling than is acknowledged generally.

      Context

      During the past century, most developed countries have witnessed a considerable rise in the prevalence of obesity.
      • Sassi F.
      • Devaux M.
      • Cecchini M.
      • Rusticelli E.
      The obesity epidemic: analysis of past and projected future trends in selected OECD countries.
      A dominant view among economists is that this trend is attributable largely to a utility-maximizing response of individuals to technologic progress that has decreased the price of energy intake (via reduced food prices) and increased the price of energy expenditure (via growing opportunity costs of physical activity).
      • Philipson T.J.
      • Posner R.A.
      The long-run growth in obesity as a function of technological change.
      Table 1 shows the impact of these changes on the costs people face when making decisions about physical activity and food consumption during their daily leisure, work, travel, and home-based activities. For example, technologic innovation in agriculture, food production, and retail has contributed to reduced costs (including time costs) of energy-dense meals, and working environments typically have become more office-based and sedentary.
      Table 1Examples of the impact of technologic progress on the costs of energy intake and energy expenditure
      Activity domainCosts of energy expenditureCosts of energy intake
      Increasing opportunity costs of energy expenditureIncreasing monetary costs of energy expenditureDecreasing costs of food consumption
      SleepN/A (The time spent sleeping has remained broadly constant)
      LeisureGreater opportunity for sedentary leisure activities (e.g., TV, computers, and the Internet)Greater availability of active leisure facilities away from home that incur a financial cost (e.g., leisure centres, swimming pools, and gyms)Increased availability of restaurants (including fast-food)
      OccupationGreater availability of, and higher wages associated with, sedentary workThe change from an agricultural or industrial society means that, in a sense, people are no longer paid to exercise at work.Greater availability of mass-produced, energy-dense, packaged, snack foods which can be consumed “on the go” (and are often heavily marketed, perhaps appealing to a lack of self-control and hyperbolic discounting which apparently characterizes food consumption)
      TransportationAvailability of motorized transport and investment in road networks has provided greater opportunities for faster and longer-distance journeys which are not well suited to active travel modesN/AExpansion of “Drive-Thru” takeaway services which allow consumption of fast-food while traveling
      HomeModern technology (e.g., gardening tools and kitchen appliances) allows household chores to be done more quickly with less physical effortN/ATransfer of labor-intensive food preparation to intensive farming, supermarkets, and factories, has dramatically reduced the costs (including time costs) associated with food preparation at home. The availability and quality of kitchen appliances such as microwaves, refrigerators, and freezers also have improved.
      N/A, not applicable
      The present paper is concerned primarily with the impact on decision making of changes in the cost of travel. Travel is a hitherto relatively under-exploited area for promoting health behavior change, but is potentially important in the “small changes approach” to tackling obesity, which focuses on small but achievable improvements in physical activity rather than more-substantial lifestyle changes that have sometimes proven unrealistic.
      • Hill J.O.
      Can a small-changes approach help address the obesity epidemic? A report of the Joint Task Force of the American Society for Nutrition, Institute of Food Technologists, and International Food Information Council.
      Because cycling and walking can be integrated more readily into people's busy schedules than, for example, leisure-time exercise,
      House of Commons Health Committee
      Third report of session 2003–04: obesity.
      • Kahlmeier S.
      • Cavill N.
      • Dinsdale H.
      • et al.
      Health economic assessment tools (HEAT) for walking and for cycling: methodology and user guide.
      these could represent low-cost, acceptable, and accessible ways to achieve 30 minutes of daily, moderate-intensity physical activity as recommended in international guidelines to help prevent obesity and more than 20 other chronic conditions.
      Department of Health
      Start active, stay active: a report on physical activity for health from the four home countries' Chief Medical Officers.
      IOM and National Research Council of the National Academies
      Local government actions to prevent childhood obesity.
      • Siegel P.Z.
      • Brackbill R.M.
      • Heath G.W.
      The epidemiology of walking for exercise: implications for promoting activity among sedentary groups.
      WHO
      Global recommendations on physical activity for health.
      • Wanner M.
      • Götschi T.
      • Martin-Diener E.
      • Kahlmeier S.
      • Martin B.W.
      Active transport, physical activity, and body weight in adults: a systematic review.
      More specifically, the current paper explores the potential for financial incentives to encourage physical activity through active travel and influence related health outcomes. Financial incentives are policies involving a targeted payment to, or withdrawal of monetary resources from, an individual's budget. They encompass interventions at the macroenvironmental (e.g., government) and microenvironmental (e.g., workplace) levels,
      • Goodman C.
      • Anise A.
      What is known about the effectiveness of economic instruments to reduce consumption of foods high in saturated fats and other energy-dense foods for preventing and treating obesity?.
      including positive financial incentives
      • Jochelson K.
      Paying the patient: improving health using financial incentives.
      rewarding active travel and negative financial incentives penalizing sedentary travel.

      Evidence Acquisition

      Identification of Relevant Studies

      The review identified studies of financial incentives relating to any mode of travel in which the impact on active travel, physical activity, or obesity levels was reported. The ECONLIT, Google Scholar, National Bureau of Economic Research (NBER) and PubMed electronic databases were searched between May 2011 and January 2012 with terms relating to “physical activity,” “transport,” “built environment,” and “prices.” Non-English-language papers, and studies published before 1997, were excluded. Five relevant reviews and 20 primary studies (of which nine were not included in the reviews) were identified (Table 2).
      Table 2Summary of evidence relating to financial incentives identified in the review
      REVIEWS
      Review referenceReviewTitle
      AMackett (2011)
      • Mackett R.
      • Brown B.
      Transport, physical activity and health: present knowledge and the way ahead.
      Transport, physical activity, and health: present knowledge and the way ahead
      BOgilvie (2004)
      • Ogilvie D.
      • Egan M.
      • Hamilton V.
      • Petticrew M.
      Promoting walking and cycling as an alternative to using cars: systematic review.
      Promoting walking and cycling as an alternative to using cars: systematic review
      COgilvie (2007)
      • Ogilvie D.
      • Foster C.E.
      • Rothnie H.
      • et al.
      Interventions to promote walking: systematic review.
      Interventions to promote walking: systematic review
      DPucher (2010)
      • Pucher J.
      • Dill J.
      • Handy S.
      Infrastructure, programs, and policies to increase bicycling: an international review.
      Infrastructure, programs, and policies to increase bicycling: An international review
      EYang (2010)
      • Yang L.
      • Sahlqvist S.
      • McMinn A.
      • Griffin S.J.
      • Ogilvie D.
      Interventions to promote cycling: systematic review.
      Interventions to promote cycling: systematic review
      STUDIES
      Study [review reference]Study designStudy descriptionResults
      Study design description (checklist score
      A higher score on the checklist represents increasing likelihood that causal inferences may be drawn. 0 = study designs from which causal inferences cannot be drawn; 1–4 = study designs from which some causal inferences may be drawn depending on the extent to which there is analysis of change over time and whether (observable and unobservable) characteristics are controlled for; 5–7 = study designs most likely to support robust causal inferences (5–6 = randomization in a natural-experiment setting; 7 = randomization in an controlled-experiment setting).
      )
      Intervention studyCountryPopulationDescription of interventionOutcomeComparatorFollow-up (months)Reported outcomesIndividual-(I) or population-(P) level data
      Travel modeActive travel or physical activityObesity, BMI or weight
      POSITIVE FINANCIAL INCENTIVES
      Walking and cycling
       Hemmingson (2009)
      • Hemmingsson E.
      • Udden J.
      • Neovius M.
      • Ekelund U.
      • Rossner S.
      Increased physical activity in abdominally obese women through support for changed commuting habits: a randomized clinical trial.
      [D,E]
      RCT (7)SwedenMiddle-aged women with abdominal obesityA moderate-intensity program including free bicyclesSignificant increase in women cycling more than 2 km per dayControl group involving a low-intensity program (excluding free bicycles)18I
       Bunde (1997)
      • Bunde J.
      The BikeBusters from Århus, Denmark: “We'll park our cars for 200 years ….”.
      [B,D]
      Uncontrolled before–after study (0)DenmarkAdultsFree bicycles (“Bikebusters”)Increase in proportion of trips made by bike (from 9% to 28%)Proportion of trips made by bike before the intervention11P
       Bauman (2008)
      • Bauman A.
      • Rissel C.
      • Garrard J.
      • Kerr I.
      • Speidel R.
      • Fishman E.
      Getting Australia moving: barriers, facilitators and interventions to get more Australians physically active through cycling.
      [A]
      Uncontrolled before–after study (0)AustraliaAdultsFree bicycles (“Cycle 100”)Increase in proportion of trips made by bikeProportion of trips made by bike before the interventionNot reportedP
       Finkelstein (2008)
      • Finkelstein E.A.
      • Brown D.S.
      • Brown D.R.
      • Buchner D.M.
      A randomized study of financial incentives to increase physical activity among sedentary older adults.
      RCT (7)U.S.Older adultsPayments contingent on exercise levels (number of “aerobic minutes”)Significant differences in exercise levelsIndividuals who receive a fixed payment irrespective of exercise levels1I
       Ryley (2006)
      • Ryley T.
      Estimating cycling demand for the journey to work or study in West Edinburgh, Scotland.
      ; Wardman (2007)
      • Wardman M.
      • Tight M.
      • Page M.
      Factors influencing the propensity to cycle to work.
      Stated Preference Data (N/A)United KingdomAdultsHypothetic payment to individuals in return for cycling more oftenIn one case, an increase in proportion of trips made by bike of 88%Hypothetic case where payments are not made to individualsN/AI
      Public transportation
       Bamberg (2006)
      • Bamberg S.
      Is a residential relocation a good opportunity to change people's travel behavior? Results from a theory-driven intervention study.
      [A]
      RCT (7)Germany, StuttgartPeople who have recently (within 6 months) moved to the citySubsidized public transport passesSignificant increases in the proportion of people using public transport and reductions in car useBefore and after the intervention (in the intervention group) and compared to respective analysis in the control group1.5I
       Lachapelle (2009)
      • Lachapelle U.
      • Frank L.D.
      Transit and health: mode of transport, employer-sponsored public transit pass programs, and physical activity.
      [A]
      Observational study (0)U.S.Workplace employeesSubsidized public transport passesSignificant increases in physical activity levelsWorkplaces that do not offer subsidized public transport passesN/A (cross-sectional study)P
       Webb (2011)
      • Webb E.
      • Netuveli G.
      • Millett C.
      Free bus passes, use of public transport and obesity among older people in England.
      Controlled study with analysis of change at individual level (4)EnglandOlder peopleSubsidized public transport passesFree pass was associated with increased public transport use. Public transport use was associated with lower obesityLogistic regression analysis using panel data24I
       Jones (2012)
      • Jones A.
      • Steinbach R.
      • Roberts H.
      • Goodman A.
      • Green J.
      Rethinking passive transport: bus fare exemptions and young people's wellbeing.
      Qualitative observational study (0)England, LondonYoung peopleSubsidized public transport passesPhysical activity increased since young people reported an increase in journeys madeYoung people's own accounts of bus travel arising from interviews and focus groupsN/AI
      NEGATIVE FINANCIAL INCENTIVES
      Walking and cycling
       Durham Council (2006)
      Durham County Council
      Saddler street user-charge monitoring report.
      [A]
      Uncontrolled before–after study (0)England, DurhamDriversRoad pricingA 10% increase in pedestrian activityBefore the road pricing was introduced9P
       Transport for London (2006)
      Transport for London
      Central London congestion charge: fourth annual monitoring report.
      [A]
      Uncontrolled before–after study (0)England, LondonDriversRoad pricingDistances cycled increased by 30%Before the road pricing was introduced36P
       Ben-Elia (2011)
      • Ben-Elia E.
      • Ettema D.
      Changing commuters' behavior using rewards: a study of rush-hour avoidance.
      ; Bliemer (2010)
      • Bliemer M.C.J.
      • Dicke-Ogenia M.
      • Ettema D.
      Rewarding for avoiding the peak period: a synthesis of four studies in the Netherlands.
      Uncontrolled before–after study (0)The Netherlands, ZoetermeerCar driversFinancial incentives of $3 to $714% of drivers switched to alternative travel modesIndividual behavior before the financial incentive was introduced3I
       Bergman (2010)
      • Bergman P.
      • Grjibovski A.M.
      • Hagstromer M.
      • Patterson E.
      • Sjostrom M.
      Congestion road tax and physical activity.
      [A]
      Uncontrolled before–after study (0)Sweden, StockholmCar drivers$2 congestion charge25% reduction in number of car journeysBefore the road pricing was introduced (and comparisons with similar cities to suggest a real effect attributable to the policy)30P
       Meland (2010)
      • Meland S.
      • Tretvik T.
      • Welde M.
      The effects of removing the Trondheim toll cordon.
      [A,B]
      Uncontrolled before–after study (0)Norway, TrondheimCar driversRemoval of a road pricing systemIncreased car journeys and decreases in public transport and active travelBefore the withdrawal of road pricingUp to 12P
       Shoup (1997)
      • Shoup D.C.
      Evaluating the effects of cashing out employer-paid parking: eight case studies.
      [B,D,E]
      Uncontrolled before–after study (0)U.S., CaliforniaCar drivers (commuters)Payment for not using a car park39% increase in active commutingBefore the schemeUp to 36P
       Rye (2002)
      • Rye T.
      Travel plans: do they work?.
      [D]
      Uncontrolled before–after study (0)England, Manchester AirportCar drivers (commuters)Car park charging (as part of a Work Place Travel Plan)A threefold increase in cyclingBefore the schemeNot reportedP
      Gasoline prices
       Rabin (2007)
      • Rabin B.A.
      • Boehmer T.K.
      • Brownson R.C.
      Cross-national comparison of environmental and policy correlates of obesity in Europe.
      Cross- sectional, observational study using linear regression (0)24 European countriesCountry-level dataNoneSignificant inverse relationship between obesity levels and obesity prevalenceCross-national comparisons are madeN/A (Cross-sectional study)P
       Courtemarche (2011)
      • Courtemanche C.
      A silver lining? The connection between gasoline prices and obesity.
      Individual- level repeated cross-sectional study (0)U.S.AdultsNoneSignificant inverse relationship between obesity levels and obesity prevalenceChanges in gas prices over time20 yearsI
       Hou (2011)
      • Hou N.
      • Popkin B.M.
      • Jacobs J.D.R.
      • et al.
      Longitudinal trends in gasoline price and physical activity: the CARDIA study.
      Random-effect longitudinal regression using individual-level data (3)U.S., four citiesYoung adults (aged 18–30 years at baseline)NoneSignificant relationship between gas prices and physical activityChanges in gas prices over time (the individuals act as their own controls)15 yearsI
       Rashad (2009)
      • Rashad I.
      Associations of cycling with urban sprawl and the gasoline price.
      Cross- sectional multivariate regression analysis (0)U.S.AdultsNoneSignificant relationship between gas prices and self-reported cyclingComparison of individuals in different areas with different gas pricesN/A (Cross-sectional study)I
      N/A, not applicable
      a A higher score on the checklist represents increasing likelihood that causal inferences may be drawn. 0 = study designs from which causal inferences cannot be drawn; 1–4 = study designs from which some causal inferences may be drawn depending on the extent to which there is analysis of change over time and whether (observable and unobservable) characteristics are controlled for; 5–7 = study designs most likely to support robust causal inferences (5–6 = randomization in a natural-experiment setting; 7 = randomization in an controlled-experiment setting).

      Data Extraction and Quality Assessment

      Information was extracted on study place and year; study design; intervention and population characteristics; and results. Quality assessment focused on the likelihood that causal inferences may be drawn,
      • Martin A.
      Evaluating causal relationships between the design of urban built environments and obesity: a systematic review UKCRC Population Health Methods and Challenges Conference.
      based on a method originally devised for use in criminology reviews.
      • Murray J.
      • Farrington D.
      • Eisner M.
      Drawing conclusions about causes from systematic reviews of risk factors: the Cambridge Quality Checklists.

      Evidence Synthesis

      Description of Studies

      The majority of studies (70%) presented evidence for a particular microenvironmental scheme. Together, only a small range of schemes were represented, predominantly involving free bicycles or local road pricing at specific locations and generally within particular population subgroups. The majority (67%) of intervention studies used uncontrolled cross-sectional analysis of population-level data, which cannot support robust causal inference. Further, most considered only changes in travel behavior or physical activity (87%), so improvements in health or reductions in obesity only can be estimated. Higher-quality study designs used included RCTs (20%), although, as with other the intervention studies, these often had short follow-up periods (average 7 months).

      Positive Financial Incentives

      Five recent reviews
      • Mackett R.
      • Brown B.
      Transport, physical activity and health: present knowledge and the way ahead.
      • Ogilvie D.
      • Egan M.
      • Hamilton V.
      • Petticrew M.
      Promoting walking and cycling as an alternative to using cars: systematic review.
      • Ogilvie D.
      • Foster C.E.
      • Rothnie H.
      • et al.
      Interventions to promote walking: systematic review.
      • Pucher J.
      • Dill J.
      • Handy S.
      Infrastructure, programs, and policies to increase bicycling: an international review.
      • Yang L.
      • Sahlqvist S.
      • McMinn A.
      • Griffin S.J.
      • Ogilvie D.
      Interventions to promote cycling: systematic review.
      that included microenvironmental interventions to promote active travel identified just three examples of positive financial incentives, all involving free bicycles. One RCT
      • Hemmingsson E.
      • Udden J.
      • Neovius M.
      • Ekelund U.
      • Rossner S.
      Increased physical activity in abdominally obese women through support for changed commuting habits: a randomized clinical trial.
      involving Swedish women with abdominal obesity reported a significant increase in the proportion of women cycling more than 2 km per day after 18 months. Two uncontrolled studies
      • Bunde J.
      The BikeBusters from Århus, Denmark: “We'll park our cars for 200 years ….”.
      • Bauman A.
      • Rissel C.
      • Garrard J.
      • Kerr I.
      • Speidel R.
      • Fishman E.
      Getting Australia moving: barriers, facilitators and interventions to get more Australians physically active through cycling.
      found that the Danish “Bikebusters” and the Australian “Cycle100” schemes led to significant increases in the proportion of trips made by bicycle (from 9% to 28% in “Bikebusters”), although both involved selected participants.
      Additional evidence, not captured in the five reviews, included an RCT
      • Finkelstein E.A.
      • Brown D.S.
      • Brown D.R.
      • Buchner D.M.
      A randomized study of financial incentives to increase physical activity among sedentary older adults.
      involving 51 older Americans in which significant differences in average daily “aerobic minutes” were identified between a group receiving fixed weekly payments of $75 and a comparison group receiving $50 plus $10 (or $25) contingent on averaging at least 15 (or 40) aerobic minutes per day each week. “Aerobic minutes” were measured using pedometers and defined as continuous walking (not necessarily for transport), jogging, or running at a rate above 60 steps per minute for at least 10 minutes. Two further studies
      • Ryley T.
      Estimating cycling demand for the journey to work or study in West Edinburgh, Scotland.
      • Wardman M.
      • Tight M.
      • Page M.
      Factors influencing the propensity to cycle to work.
      reported stated preference data. One
      • Wardman M.
      • Tight M.
      • Page M.
      Factors influencing the propensity to cycle to work.
      of these showed that a £2 daily payment to cyclists could increase cycling by 88%, although these studies relied on individuals choosing between hypothetic alternatives.
      Many studies in transport economics have shown a negative price elasticity of demand for public transport,
      • Paulley N.
      • Balcombe R.
      • Mackett R.
      • et al.
      The demand for public transport: the effects of fares, quality of service, income and car ownership.
      indicating that price reductions would lead to increased demand. If, as three studies
      • Bamberg S.
      Is a residential relocation a good opportunity to change people's travel behavior? Results from a theory-driven intervention study.
      • Lachapelle U.
      • Frank L.D.
      Transit and health: mode of transport, employer-sponsored public transit pass programs, and physical activity.
      • Webb E.
      • Netuveli G.
      • Millett C.
      Free bus passes, use of public transport and obesity among older people in England.
      show, this displaces car journeys (rather than active travel), then increased physical activity would be expected because public transport use typically is accompanied by some walking.
      • Besser L.M.
      • Dannenberg A.L.
      Walking to public transit: steps to help meet physical activity recommendations.
      • Edwards R.D.
      Public transit, obesity, and medical costs: assessing the magnitudes.
      • MacDonald J.M.
      • Stokes R.J.
      • Cohen D.A.
      • Kofner A.
      • Ridgeway G.K.
      The effect of light rail transit on body mass index and physical activity.
      • Morabia A.
      • Mirer F.E.
      • Amstislavski T.M.
      • et al.
      Potential health impact of switching from car to public transportation when commuting to work.
      At the microenvironmental level, in the first study,
      • Bamberg S.
      Is a residential relocation a good opportunity to change people's travel behavior? Results from a theory-driven intervention study.
      an RCT reported significant increases in the proportion of people using public transport (from 18% to 47%) and reductions in car use (from 50% to 33%) in an intervention group that received free public transport passes in Stuttgart, Germany. Respective changes in the control group were not significant and there were no changes in cycling or walking trips. In the second study,
      • Lachapelle U.
      • Frank L.D.
      Transit and health: mode of transport, employer-sponsored public transit pass programs, and physical activity.
      higher employee physical activity levels were shown in U.S. workplaces that provided subsidized public transport passes compared to those that did not. However, the effect may have been over-estimated because workplaces were more likely to provide a subsidy if public transport facilities were within walking distance.
      At the macroenvironmental level, the impact of free bus passes, available to older people in England since 2006, was examined using a logistic regression analysis of the English Longitudinal Study of Ageing (ELSA).
      • Webb E.
      • Netuveli G.
      • Millett C.
      Free bus passes, use of public transport and obesity among older people in England.
      Eligibility for the free pass was associated with a 51% increase in the odds of using public transport, whereas public transport use in old age was associated with 21% lower odds of being obese, even after adjustment for previous weight status. A fourth study,
      • Jones A.
      • Steinbach R.
      • Roberts H.
      • Goodman A.
      • Green J.
      Rethinking passive transport: bus fare exemptions and young people's wellbeing.
      of free bus passes available to young people in London, England, since 2008, showed that although increased public transport demand displaced some active travel journeys, physical activity increased because the pass generated more journeys overall.

      Negative Financial Incentives

      At the microenvironmental level, one review
      NICE Public Health Collaborating Centre—Physical activity
      Physical activity and the environment: transport review.
      identified limited evidence from two intervention studies about the impact of road-user charging on physical activity. In Durham, England,
      Durham County Council
      Saddler street user-charge monitoring report.
      a 10% increase in pedestrian activity was reported 1 year after the scheme started, and in London,
      Transport for London
      Central London congestion charge: fourth annual monitoring report.
      distances cycled increased by 30% over a 3-year period.
      In Zoetermeer, The Netherlands, a study showed that 14% of car drivers switched to alternative travel modes after daily financial incentives of €3 to €7 were given to regular commuters in return for avoiding specific road sections.
      • Ben-Elia E.
      • Ettema D.
      Changing commuters' behavior using rewards: a study of rush-hour avoidance.
      • Bliemer M.C.J.
      • Dicke-Ogenia M.
      • Ettema D.
      Rewarding for avoiding the peak period: a synthesis of four studies in the Netherlands.
      In Stockholm, Sweden, another study
      • Bergman P.
      • Grjibovski A.M.
      • Hagstromer M.
      • Patterson E.
      • Sjostrom M.
      Congestion road tax and physical activity.
      found a 25% reduction in the number of car journeys in response to a temporary $2 congestion charge. Small increases in public transport use and self-reported physical activity levels also were identified. In Trondheim, Norway, one study
      • Meland S.
      • Tretvik T.
      • Welde M.
      The effects of removing the Trondheim toll cordon.
      attributed an increase in car journeys and decreases in public transport use, cycling, walking, and car occupancy to the withdrawal of road pricing.
      Other microenvironmental evidence includes a study
      • Rye T.
      Travel plans: do they work?.
      reporting a threefold increase in cycling among employees at Manchester Airport, England, attributed to a Workplace Travel Plan that included increased car parking charges, and other reports
      • Cairns S.
      • Davis A.
      • Newson C.
      • Swiderska C.
      Making travel plans work: research report.
      that those Workplace Travel Plans which included car-sharing financial incentives had the greatest chance of reducing car use. A further study
      • Shoup D.C.
      Evaluating the effects of cashing out employer-paid parking: eight case studies.
      of eight California workplaces reported a 39% increase in active commuting attributable to “cashing out,” in which individuals receive payment for not using their free workplace car parking space. However, these three studies were poorly controlled and the changes were small in absolute terms.
      At the macroenvironmental level, two studies
      • Rabin B.A.
      • Boehmer T.K.
      • Brownson R.C.
      Cross-national comparison of environmental and policy correlates of obesity in Europe.
      • Courtemanche C.
      A silver lining? The connection between gasoline prices and obesity.
      identified a significant inverse relationship between gasoline prices and obesity prevalence (defined as the proportion of individuals with a BMI ≥30). The first
      • Rabin B.A.
      • Boehmer T.K.
      • Brownson R.C.
      Cross-national comparison of environmental and policy correlates of obesity in Europe.
      drew cross-national comparisons of 24 European countries. Using U.S. data, the second
      • Courtemanche C.
      A silver lining? The connection between gasoline prices and obesity.
      suggested that 8% of the rise in obesity prevalence between 1979 and 2004 was attributable to declining gasoline prices (via reduced walking and increased restaurant visits). It implied that a $1/gallon gasoline tax would reduce obesity prevalence by 10%, with some evidence that women, ethnic minorities, and lower-income groups were most responsive to price changes (although this may have been due to their living in urban areas with public transport facilities).
      One study
      • Hou N.
      • Popkin B.M.
      • Jacobs J.D.R.
      • et al.
      Longitudinal trends in gasoline price and physical activity: the CARDIA study.
      involving 20 years' worth of cohort data from 5115 U.S. individuals demonstrated a positive association between gasoline prices and physical activity. Roughly, there were 17 minutes of additional walking each week after a $0.25 per gallon increase. The study also suggested that the price change might encourage individuals to replace physical activity away from home (e.g., bowling) with activities in the immediate area (e.g., jogging).
      Econometric analysis also has been used to show an inverse relationship between gasoline taxation and gasoline consumption.
      • Sterner T.
      Fuel taxes: an important instrument for climate policy.
      One review
      • Goodwin P.
      • Dargay J.
      • Hanly M.
      Elasticities of road traffic and fuel consumption with respect to price and income: a review.
      estimated that a 10% rise in gasoline prices was associated with reductions of 3% in road traffic and 2.5% in car ownership. Although more active travel cannot be inferred, because car trips are less responsive to gasoline prices than fuel consumption and distance traveled,
      • Graham D.J.
      • Glaister S.
      Road traffic demand elasticity estimates: a review.
      some studies did report a positive relationship between gasoline prices and demand for other travel modes.
      • Goodwin P.
      • Dargay J.
      • Hanly M.
      Elasticities of road traffic and fuel consumption with respect to price and income: a review.
      For example, one U.S. study
      • Rashad I.
      Associations of cycling with urban sprawl and the gasoline price.
      used self-reported data from a national survey to claim that cycling increased by 4.7% for men and 3.5% for women after a $1 per gallon gas price increase.

      Summary

      This review identified only a limited amount of evidence on financial incentives for active travel. Although the identified studies provide useful insights into specific interventions for particular populations, a more general understanding about how people might be expected to respond has yet to emerge.

      Discussion

      One partial explanation for the shortage of empirical evidence, particularly at the macroenvironmental level, may be the potential political risks generally associated with financial incentives.
      • Mackett R.
      • Brown B.
      Transport, physical activity and health: present knowledge and the way ahead.
      • Wise J.
      NICE citizens council debates incentives for healthy behaviour.
      • Parke H.
      • Ashcroft R.
      • Brown R.
      • Marteau T.M.
      • Seale C.
      Financial incentives to encourage healthy behaviour: an analysis of UK media coverage.
      Negative financial incentives typically require strong justification because they penalize individuals who happen to have made particular choices, whereas positive financial incentives require substantial financial investment.
      House of Lords Science and Technology Select Committee
      2nd report of session 2010–12: behaviour change.
      Nuffield Council on Bioethics
      Public health: ethical issues.
      However, financial incentives for active travel could be viewed somewhat more favorably as they fall neatly between regulating (or “nannying”), which is sometimes regarded as overly restricting choice, and interventions that provide feedback (or “nudging”), which might not be highly effective when used in isolation
      • Marteau T.M.
      • Ogilvie D.
      • Roland M.
      • Suhrcke M.
      • Kelly M.P.
      Judging nudging: can nudging improve population health?.
      (Figure 1,
      • de Grange L.
      • Troncoso R.
      Impacts of vehicle restrictions on urban transport flows: the case of Santiago, Chile.
      ,
      • Woodcock J.
      • Banister D.
      • Edwards P.
      • Prentice A.M.
      • Roberts I.
      Energy and transport.
      ). They also could reinforce existing government priorities such as environmental sustainability, tackling health inequalities, and economic growth (via reduced congestion and absenteeism). Further, implementation may prove relatively straightforward if integrated somehow with existing transport schemes designed to internalize externalities including congestion, injuries, pollution,
      • Timilsina G.R.
      • Dulal H.B.
      Urban road transportation externalities: costs and choice of policy instruments.
      and even risky driving.
      • Zantema J.
      • van Amelsfort D.
      • Bliemer M.
      • Bovy P.
      Pay-as-you-drive strategies: case study of safety and accessibility effects.
      Relevant lessons also might be drawn from financial incentives used in health care to reduce smoking, alcohol, and obesity
      • Marteau T.M.
      • Ashcroft R.E.
      • Oliver A.
      Using financial incentives to achieve healthy behaviour.
      ; improve patient compliance
      • Giuffrida A.
      • Torgerson D.J.
      Should we pay the patient? Review of financial incentives to enhance patient compliance.
      ; and encourage Chlamydia screening.
      • Currie M.J.
      • Schmidt M.
      • Davis B.K.
      • et al.
      “Show me the money”: financial incentives increase chlamydia screening rates among tertiary students: a pilot study.
      Figure thumbnail gr1
      Figure 1A hierarchy of policy interventions to support active travel
      Note: Higher rungs on the ladder represent decreasing acceptability and increasing intrusiveness (as suggested in the Nuffield Intervention Ladder
      Nuffield Council on Bioethics
      Public health: ethical issues.
      ). Decision makers should only consider policies on higher rungs of the ladder if policies on lower rungs are deemed to be ineffective.
      To gain a more comprehensive understanding of the complex individual-level impact of financial incentives on travel behavior and health, higher-quality studies that support more-robust causal inference are required. Reliance on uncontrolled cross-sectional studies with short follow-up periods particularly limits the potential for understanding downstream changes, such as body size, or how to prevent people from returning to old habits after financial incentives are withdrawn.
      • Jochelson K.
      Paying the patient: improving health using financial incentives.
      • Mackett R.
      • Brown B.
      Transport, physical activity and health: present knowledge and the way ahead.
      • Ettema D.
      • Knockaert J.
      • Verhoef E.
      Using incentives as traffic management tool: empirical results of the “peak avoidance” experiment.
      Such studies also may have limited external validity if they include only small population subsets, such as ethnic minority, low-income groups in high-density urban areas (one study shows that walking to public transport is especially common in these groups),
      • Besser L.M.
      • Dannenberg A.L.
      Walking to public transit: steps to help meet physical activity recommendations.
      or people who have recently moved.
      • Bamberg S.
      Is a residential relocation a good opportunity to change people's travel behavior? Results from a theory-driven intervention study.
      • Sloman L.
      • Cairns S.
      • Newson C.
      • Anable J.
      • Pridmore A.
      • Goodwin P.
      The effects of smarter choice programmes in sustainable travel towns: a research report.
      Further, biased effect estimates can occur if the quality of the built environment, which may support or hinder active travel,
      • Fraser S.D.S.
      • Lock K.
      Cycling for transport and public health: a systematic review of the effect of the environment on cycling.
      • Jones A.
      • Bentham G.
      • Foster C.
      • Hillsdon M.
      • Panter J.
      Tackling obesities: future choices; obesogenic environments—evidence review.
      or other factors, such as climate or the supportiveness of employers, are not controlled for.
      Although RCTs may sometimes be unrealistic or politically untenable,
      • Macintyre S.
      Evidence based policy making.
      “natural experiment” designs, in which a “natural or predetermined variation of allocation occurs,”
      • Petticrew M.
      • Cummins S.
      • Ferrell C.
      • et al.
      Natural experiments: an underused tool for public health?.
      Medical Research Council
      Using natural experiments to evaluate population health interventions.
      provide a promising alternative. These include intervention studies with large individual-level data sets, such as those proposed for the evaluation of various policy and infrastructure projects in the United Kingdom,
      • Jones A.
      • Steinbach R.
      • Roberts H.
      • Goodman A.
      • Green J.
      Rethinking passive transport: bus fare exemptions and young people's wellbeing.
      • Ogilvie D.
      • Bull F.
      • Powell J.
      • et al.
      iConnect Consortium
      An applied ecological framework for evaluating infrastructure to promote walking and cycling: the iConnect Study.
      • Ogilvie D.
      • Griffin S.
      • Jones A.
      • et al.
      Commuting and health in Cambridge: a study of a “natural experiment” in the provision of new transport infrastructure.
      and non-intervention studies relating particularly to negative financial incentives, which rely mainly on observed relationships between population-level behavior and price changes over time. Although the latter provide a weaker basis for causal inference, similar econometric evidence supported the initial case for tobacco taxation.
      • Chaloupka F.J.
      • Warner K.E.
      The economics of smoking.
      With appropriate data, these methods also can contribute to a deeper understanding of the distribution of health benefits across various population groups and provide important insights into the types of financial incentives most likely to deliver long-term behavior change.

      Other Insights from Economic Rational-Choice Frameworks

      Appendix A describes how an economic rational-choice framework might be developed to draw some broader insights into people's likely responses to financial incentives for active travel. It incorporates elements of the SLOTH time-budget model,
      • Cawley J.
      An economic framework for understanding physical activity and eating behaviors.
      • Frank L.D.
      Economic determinants of urban form: resulting trade-offs between active and sedentary forms of travel.
      • Pratt M.
      • Macera C.A.
      • Sallis J.F.
      • O'Donnell M.
      • Frank L.D.
      Economic interventions to promote physical activity: application of the SLOTH model.
      and Lakdawalla-Philipson's utility maximization model,
      • Lakdawalla D.
      • Philipson T.
      The growth of obesity and technological change.
      developed elsewhere for analyzing the multitude of decisions people make when allocating scarce resources of time and money to competing demands. This analysis provides a useful illustration of two broad points that were not established in the literature review and are in some contrast to existing SLOTH-based analyses which suggest that “leisure becomes the most likely area for increasing physical activity”
      • Pratt M.
      • Macera C.A.
      • Sallis J.F.
      • O'Donnell M.
      • Frank L.D.
      Economic interventions to promote physical activity: application of the SLOTH model.
      because (for simplicity) the trade-offs associated with leisure and travel decisions have been treated as though identical.
      First, the framework suggests that individuals are likely to be at least as (if not more) responsive to financial incentives for active travel as those for active leisure, a view reflected in recent panel data analysis that shows active leisure “comes and goes” and “exercise as part of travel and work must be emphasized.”
      • Popham F.
      • Mitchell R.
      Leisure time exercise and personal circumstances in the working age population: longitudinal analysis of the British household panel survey.
      Second, active travel allows people to access work and leisure activities but, unlike sedentary travel, is also “productive” in the sense of enabling energy expenditure. Yet established methods for transport appraisal place large monetary values on travel-time savings to justify investment in transport infrastructure on the basis that (for travel in work hours) savings in travel time convert nonproductive time to productive use.
      Department for Transport
      Values of time and operating costs.
      • Jain J.
      • Lyons G.
      The gift of travel time.
      • Mokhtarian P.L.
      • Salomon I.
      How derived is the demand for travel? Some conceptual and measurement considerations.
      In contrast to car travel, others have argued that this overlooks the potential to use rail travel productively for work activities.
      • Lyons G.
      • Urry J.
      Travel time use in the information age.
      • Lyons G.
      • Jain J.
      • Holley D.
      The use of travel time by rail passengers in Great Britain.
      Similarly, these methods probably favor faster sedentary travel (cars and trains) over active travel, despite active travel being suitable for most journeys.
      • Dora C.
      A different route to health: implications of transport policies.
      These methods also may have encouraged decline in the availability of local services that are particularly accessible by active travel. In the United Kingdom, where travel-time savings have accounted for around 80% of the claimed monetary benefits of major road schemes, the average time that people spend traveling has remained constant since the 1960s.
      • Metz D.
      The myth of travel time saving.
      This suggests that motorway (freeway) expansion has encouraged long-distance travel for access to work and leisure opportunities much farther from home. People who choose active travel may then experience mobility-related social exclusion,
      • Lyons G.
      • Urry J.
      Travel time use in the information age.
      where they are disadvantaged in terms of access to services.
      In the absence of more empirical evidence, further development of a modeling approach to active-travel decisions may prove advantageous; however psychological theories of behavior and recent empirical work in behavioral economics should be incorporated alongside standard rational behavior assumptions.
      • Cutler D.
      • Glaeser E.
      • Shapiro J.
      Why have Americans become more obese?.
      • Dolan P.
      • Hallsworth M.
      • Halpern D.
      • King D.
      • Vlaev I.
      MINDSPACE: influencing behaviour through public policy.
      • Ruhm C.J.
      Understanding overeating and obesity.
      For example, overly self-focused behavior,
      • Van Vugt M.
      • Van Lange P.A.M.
      • Meertens R.M.
      Commuting by car or public transportation? A social dilemma analysis of travel mode judgements.
      strong habitual behavior, optimism bias, and ingrained social norms may all favor motorized transport and discourage individuals from giving rational consideration to active travel modes.
      • Young S.
      • Caisey V.
      Mind shift, mode shift: a lifestyle approach to reducing car ownership and use based on behavioural economics and social marketing.
      The resulting “car dependency” may be reinforced by car manufacturers through marketing and political lobbying.
      • Douglas M.J.
      • Watkins S.J.
      • Gorman D.R.
      • Higgins M.
      Are cars the new tobacco?.
      These factors, and policies for moderating them, are explored in Figure 2 in the context of the theory that individual behavior is determined by a deliberative system, which assesses options with a broad, goal-based perspective, and an affective system that encompasses emotions and motivational drives.
      • Loewenstein G.F.
      • O'Donoghue T.
      Animal spirits: affective and deliberative processes in economic behavior.
      The deliberative system is described in Ajzen's theory of planned behavior as comprising attitudes, subjective norms, and perceived behavioral control.
      • Ajzen I.
      The theory of planned behavior.
      For example, the Cycling Demonstration Towns program in England, in which per capita investment in schemes to promote cycling was increased in six urban areas to ten times the national average,
      • Sloman L.
      • Cavill N.
      • Cope A.
      • Muller L.
      • Kennedy A.
      Analysis and synthesis of evidence on the effects of investment in six cycling demonstration towns.
      might be viewed as a method of influencing habitual behavior (“changing the default”) and “status quo bias,” where people tend to maintain established behaviors unless incentives to change are substantial. However, studies specifically examining the impact of financial incentives on habitual travel behavior have produced inconclusive results.
      • Bamberg S.
      Is a residential relocation a good opportunity to change people's travel behavior? Results from a theory-driven intervention study.
      • Thøgersen J.
      • Møller B.
      Breaking car use habits: the effectiveness of a free one-month travelcard.
      Figure thumbnail gr2
      Figure 2Alternative theoretic perspectives on travel mode choices and active travel policies
      In addition to habitual behavior, excessive driving also might occur because people feel they ought to drive more often in order to justify the high sunk (i.e., retrospective and nonrecoverable) costs they incurred when buying a car. Like rail commuters with annual season tickets,
      • Simma A.
      • Axhausen K.
      Commitments and modal usage: analysis of German and Dutch Panels.
      they find that additional journeys incur low marginal costs. Yet, when encouraged to consider only the (smaller) average cost of each journey, the utility-maximizing allocation of resources would involve more active travel.
      Although the evidence is limited, “car clubs,” in which car drivers hire cars for short periods rather than owning them outright, are reported to have reduced car mileage (by 33% in The Netherlands),
      • Cairns S.
      • Sloman L.
      • Newson C.
      • Anable J.
      • Kirkbride A.
      • Goodwin P.
      Smarter choices: changing the way we travel.
      increased cycling,
      • Steininger K.
      • Vogl C.
      • Zettl R.
      Car-sharing organizations: the size of the market segment and revealed change in mobility behavior.
      and reduced motor vehicle ownership.
      • Martin E.
      • Shaheen S.A.
      • Lidicker J.
      Carsharing's impact on household vehicle holdings: results from a North American shared-use vehicle survey.
      Bicycle hire schemes might have a similar impact in the sense that car drivers are not deterred by the monetary and other costs (e.g., those arising from unfamiliarity) of a bike purchase. In the Netherlands, a before-and-after study has attributed reductions in car use and increases in cycling to such schemes.
      • Martens K.
      Promoting bike-and-ride: the Dutch experience.
      Public transport “clubs,” which encourage passengers to consider marginal (rather than average) costs by making a large upfront payment for future discounted public transport tickets, also have encouraged higher tram and bus use in some Swiss cities,
      • FitzRoy F.
      • Smith I.
      Season tickets and the demand for public transport.
      although any association with fewer car journeys is unknown.

      Conclusion

      Recent empirical evidence, complemented by a simple economic rational-choice framework, suggests that financial incentives for active travel may represent an underused but potentially promising method for encouraging healthier behaviors. However, higher-quality studies, particularly at the macroenvironmental level, are required if policymakers are to use evidence of effectiveness to make confident decisions about allocating scarce resources to such schemes.
      The authors were supported by the Centre for Diet and Activity Research (CEDAR), a UKCRC Public Health Research Centre of Excellence. Funding from the British Heart Foundation, Economic and Social Research Council, Medical Research Council, the National Institute for Health Research, and the Wellcome Trust, under the auspices of the UK Clinical Research Collaboration, is gratefully acknowledged. David Ogilvie is supported also by the Medical Research Council [Unit Programme number U106179474 ].
      No financial disclosures were reported by the authors of this paper.

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