The impact of fare-free public transport on travel behavior
Last registered on December 24, 2018


Trial Information
General Information
The impact of fare-free public transport on travel behavior
Initial registration date
December 21, 2018
Last updated
December 24, 2018 4:33 AM EST
Primary Investigator
Other Primary Investigator(s)
PI Affiliation
PI Affiliation
Additional Trial Information
Start date
End date
Secondary IDs
We investigate the impact of fare-free public transport on travel behavior. We randomly assigned a public transportation pass to individuals working in Santiago (Chile) that allowed them unlimited travel without paying and evaluated its effects over two weeks. The results show that access to fare-free public transport increased the total number of trips, regardless of the mode, by 11%. Interestingly, this trip generation effect is mostly driven by an increase in the number of trips made by modes other than public transport. The average treatment effect public transport trips is positive yet not significant. Therefore we find evidence of a trip generation effect, that there is no transport-mode substitution and, as a consequence, no evidence that fare-free public transport reduces negative externalities from car travel.
External Link(s)
Registration Citation
Bull, Owen, Juan Muñoz and Hugo Silva. 2018. "The impact of fare-free public transport on travel behavior." AEA RCT Registry. December 24.
Experimental Details
Intervention Start Date
Intervention End Date
Primary Outcomes
Primary Outcomes (end points)
Total trips; trips made by public transport; trips made by modes other than public transport.
Primary Outcomes (explanation)
Number of trips taken in a two-week period
Secondary Outcomes
Secondary Outcomes (end points)
Secondary Outcomes (explanation)
Experimental Design
Experimental Design
The focus of our study was the Santiago labor force, which was selected as our group of interest for many reasons. First, commuting trips are a large share of the trips in Santiago. Commuting represents 74% of the morning peak trips, and 42% of the commuting trips are made by public transport. Commuting trips are also important within the public transport system, as they represent 44% of the total number of trips made by public transport in Santiago in a workday.

The evaluation was done in 13 firms in two periods. The first period began in October 2016 with three employers and the second period started in March 2017 with the remaining ten firms. People within each firm applied for participation in the experiment by filling a survey about their basic information and socioeconomic characteristics. Selection of people for participation in the trial was aimed at individuals whose working schedules displayed enough regularity, such as working every week, to ensure some degree of comparability between the work weeks covered by the study period. We excluded individuals who already enjoyed government-financed fare discounts. Participants were requested to record every trip they took in a trip diary, documenting the trip purpose, start time (departure from place of activity), end time (arrival at destination), the location of destination (the district in Santiago) and mode of transport.

The randomization was carried out at the individual level in each of the 13 firms after the first week of recording trips. Participants assigned to the treatment group were given a public transport card that allowed them to travel on the entire public transport system (including buses and metro) for two weeks without paying. Participants in the control group were given a lump-sum transfer at the end of the experiment of US $22.5. Stratified randomization was performed within each firm, when the sample size was big enough to allow for it, according to the participants' intensity of public transport use (measured on their Santiago fare card data for the 90 days immediately previous to the study period).
Experimental Design Details
Randomization Method
Randomization done in an office by a computer
Randomization Unit
Randomization at the individual level
Was the treatment clustered?
Experiment Characteristics
Sample size: planned number of clusters
13 firms
Sample size: planned number of observations
200 individuals
Sample size (or number of clusters) by treatment arms
101 individuals as control and 106 individuals treated with a two-week public transport pass
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
Outcome: total trips made by public transport. MDE=1,329701715, SD=2,986540139; 80% power. Outcome: total trips. MDE=1,451911425, SD=3,261025912; 80% power. Outcome: total trips in modes other than public transport. MDE=1,582815793, SD=3,555040084; 80% power.
IRB Name
IRB Approval Date
IRB Approval Number
Post Trial Information
Study Withdrawal
Is the intervention completed?
Is data collection complete?
Data Publication
Data Publication
Is public data available?
Program Files
Program Files
Reports and Papers
Preliminary Reports
Relevant Papers