We screened 5606 references and assessed the full text of 399 documents in seven languages (see figure on bmj.com
). Twenty two studies met our inclusion criteria: three randomised controlled trials, seven non-randomised controlled prospective studies, 11 uncontrolled prospective studies, and one controlled retrospective study. We categorised studies according to the main focus of the intervention assessed. Within each intervention category, we have reported interventions in decreasing order of overall study validity, citing results of statistical tests if authors reported them or if we could estimate confidence intervals from reported data (). Additional data can be found in table C on bmj.com
Summary of evidence of effectiveness of interventions to promote modal shift
Targeted behaviour change programmes (six studies of four interventions)
These programmes aimed to change people's travel behaviour by offering an intervention only to a motivated subgroup of the population or by offering information and advice tailored to people's particular requirements, or both.
The Walk In to Work Out self help package in Glasgow (Scotland) was evaluated in a randomised controlled trial in commuters identified as contemplating or actively preparing to change their behaviour. After six months, the intervention group reported an increase in mean time spent walking to work each week 1.93 (95% confidence interval 1.06 to 3.52) times greater than in people in the control group.w1 w2 In the TravelSmart programme, households interested in changing their behaviour were given a tailored selection of resources such as leaflets, timetables, maps, and free trial bus tickets. A controlled repeated cross sectional study of a sample of all households in one area in Perth (Australia) found a positive shift of 5.5% of all trips (P < 0.01) in the intervention area after six months compared with a 2% shift towards the car in a neighbouring control area.w3-9 Subsequent controlled pilots in Fromew10 and Gloucesterw11 (England) also found net positive shifts (3.6% and 4.4% respectively).
Calculation of a common primary outcome metric
We found that studies had used various metrics for expressing data relevant to our primary outcome measure. We could not identify a single common metric with which to synthesise the results of all relevant studies, but where possible we did summarise effects on the overall distribution of transport choices as follows.
We calculated the absolute change in the percentage share of all trips that were made by walking and cycling combined and compared this with the absolute change in the percentage share of all trips that were made by car. If the two changes were in opposite directions, we took the smaller of the two changes and used this to summarise the absolute shift from the car to the physically active modes. For example, if the percentage share of car trips decreased from 50% to 40% of all trips, and the percentage share of walking and cycling trips combined increased from 20% to 25%, we summarised this as a positive modal shift of 5% of all trips from a baseline share of 20%. If the two changes were in the same direction (if, for example, the public transport share of all trips increased at the expense of car, walking, and cycling trips) we summarised this as a modal shift of zero.
In Århus (Denmark), volunteer suburban car commuters were given a free bike and bus pass for a year in the Bikebusters programme. In an uncontrolled study, participants reported a positive shift of 25% of all weekday trips after 11 months.w12-14 In the Travel Blending programme, households in two areas in Adelaide (Australia) were given tailored feedback on personal travel diaries, supported with information such as timetables or maps. In an uncontrolled panel study, households reported small changes (1.0% and -2.0%, respectively) in walking trips and larger but inconsistent changes in cycling trips after one month.w15-18
Agents of change and publicity campaigns (four studies)
These interventions were applied to whole groups of people undifferentiated by motivation or personal travel circumstances. A cluster randomised controlled trial in primary schools in Camden and Islington (London) found that pupils in 10 intervention schools that received one year's input from a school travel coordinator were no less likely to travel to school by car than those in control schools (odds ratio 0.98, 95% confidence interval 0.61 to 1.59).w19 In Maidstone (England), a controlled repeated cross sectional study of households on trunk route corridors showed that two years after a publicity campaign on sustainable transport, the only significant change was a decrease in cycling trips in the intervention area (P < 0.05).w20
Drivers responding to an uncontrolled repeated cross sectional telephone survey in Phoenix (Arizona, USA) reported a positive shift of 1% of commuting journeys seven months after the Clean Air Force campaign to promote not driving to work one day a week.w21 In the Curb Your Car campaign, transport coordinators organised promotional events and distributed free bus passes at state workplaces in Eugene (Oregon). An uncontrolled repeated cross sectional study found no evidence of a shift in employees' usual mode of travel to work after nine months.w22
Engineering measures (six studies)
Repeated cross sectional household studies in Delft (Netherlands; controlled study) and Detmold and Rosenheim (Germany; uncontrolled study) evaluated the effects of improving and extending cycle route networks. In Delft, households in the intervention suburb reported a 3% increase after three years in the share of all trips made by bike, with no change in the shares for walking or car use; in the control area, the frequency of car trips increased and the frequency of bike trips did not change. A nested panel study found a positive shift of 0.6% of all trips.w23-30 In Detmold and Rosenheim, households reported a negative shift of 5% of all trips (Detmold) and zero shift (Rosenheim) after five years.w31-33
An uncontrolled repeated cross sectional study in secondary school pupils in Stockton (England) reported a negative shift of 2% in their usual mode of travel to school 17 months after a new cycle route was opened in the town.w34 Also in England, traffic restraint schemes were evaluated in uncontrolled studies of 20 miles (30 km) per hour zones in six urban neighbourhoods and of the Bypass Demonstration Project in six small towns. There was no evidence of a change in travel patterns in a panel study of residents of the 20 miles per hour zones,w35 and a repeated cross sectional survey of residents of the bypassed towns found a negative shift of 3% in their main mode of travel to the town centre.w36-37
Office workers in an uncontrolled repeated cross sectional study in Boston (USA) reported a positive shift of less than 1% of commuting journeys after the introduction of the downtown auto restricted zone.w38-40
Financial incentives (two studies)
A controlled repeated cross sectional study in California evaluated a directive to “cash out” the cost of subsidising workplace parking (by offering at least equivalent subsidies to staff who commute by modes other than driving). Employees at eight intervention workplaces reported a positive shift of 1% of commuting journeys after one to three years (P < 0.01) compared with no significant change in one control workplace.w41 w42 In Trondheim (Norway), a toll ring was introduced for motor vehicles around the city centre. An uncontrolled household panel study found a negative shift of 2.6% of all trips after one year.w43 w44
Providing alternative services (three studies)
A controlled repeated cross sectional study of the City CarShare club in San Francisco (USA) found that members were no more likely to report a positive shift after nine months than aspiring members still waiting to join. The share of journeys made by car increased by a greater proportion than the combined walking and cycling mode share did (17.0% and 3.7%, respectively).w45-47
In Voorhout (a commuter town in the Netherlands), an uncontrolled household panel study found a positive shift of 5.0% of all trips (P < 0.001) one year after the first train station was opened in the town.w48 A controlled retrospective study of commuters registered with neighbourhood telecommuting centres in California (USA) found a negative shift of 0.2% on telecommuting days compared with normal commuting days, with a 24% decrease in reported distance travelled on foot or by bike.w49
Effects on health (six studies)
We found robust evidence of effects on health in only two randomised controlled trials of the effects of active commuting in selected volunteers (see table D on bmj.com
). The Walk in to Work Out trial in Glasgow (Scotland) showed significant net increases in sample mean scores on the mental health, vitality, and general health subscales of the SF-36 after six months.w1
A smaller trial in Tampere (Finland) showed significant net improvements in maximum aerobic power, maximum treadmill time, and heart rate and blood lactate concentrations at submaximal standard workload after 10 weeks.w50 w51
We also found data on road traffic incidents and other aspects of community health, but only from small studies of relatively low validity of interventions not shown to be effective in promoting a shift in mode of transport.w34-37
Social distribution of effects (11 studies)
Findings on social distribution of effects were generally reported briefly or without the data on which statements were based, or both. The data were insufficient to permit any meaningful synthesis (see table E on bmj.com