The researchers recruited over two thousand public service vehicles (PSVs) and randomly assigned half to receive five stickers, based on the last digit of the vehicle’s license plate; if it was odd, the vehicle was assigned to receive the stickers; if it was even, it did not receive any stickers.

Drivers of PSVs assigned to stickers were asked to place them inside vehicles on the metal panel between the passenger windows and the ceiling, ensuring that at least one was in eye-view of the passengers.  Two of the stickers used fear as a motivator by displaying both images of dismembered limbs and text encouraging individuals to speak up if the driver wasn’t driving safely. The other three stickers only included text prompting individuals to speak up.

The drivers of those vehicles were incentivized to keep the stickers in place through a weekly lottery, in which vehicles were randomly selected for inspection. If they had all of their stickers in place, the driver won a monetary award ranging from $25 to $60, which corresponds to roughly a week’s wages. The researchers partnered with the companies providing insurance to almost all matatus in their sample to follow the vehicles for 17 months after recruitment, and obtain insurance claims data for vehicles in both groups.  They also collected the same information for the sample vehicles for a period of a year and a half prior to the start of the intervention.

The randomized evaluation found that posting stickers encouraging passengers to speak up about reckless driving resulted in a 7.3 percentage point reduction in the insurance claims rate, and a 6.8 percentage point reduction in claims for accidents where the driver was at fault, compared to vehicles with no stickers. The researchers estimate that among drivers who complied with the sticker assignment, around three-quarters of the accidents that would otherwise have occurred were avoided.

Furthermore, the researchers estimate that their small-scale intervention of just 17 months saved 1200 years of life. Since the intervention cost only $7/vehicle for each year, they find that the cost per life year saved using the sticker intervention is $14.5, placing it among some of the most cost-effective life-saving interventions. Taking into account the impact on prevented injuries as well, it could go down to under ten dollars per life year saved.

Inspired to implement this design in your own work? Here are some things to think about before you get started:

• Are the behavioral drivers to the problem you are trying to solve similar to the ones described in the challenge section of this project?
• Is it feasible to adapt the design to address your problem?
• Could there be structural barriers at play that might keep the design from having the desired effect?
• Finally, we encourage you to make sure you monitor, test and take steps to iterate on designs often when either adapting them to a new context or scaling up to make sure they’re effective.

Additionally, consider the following insights from the design’s researchers:

• Survey stakeholders to find out what interventions could be effective. The research team spoke with matatu riders prior to designing the intervention and found that drawing attention to reckless driving was likely to be effective in this situation.
• Try to account for how the intervention will affect all relevant individuals. Two of the stickers designed to frighten riders with graphic images were so alarming that some drivers refused to place them in their vehicles!
• If possible, try out the intervention on a small scale first. The researchers first tried a different randomization method and lottery set-up with a small subset of individuals before settling on the final design.
• While most individuals complied with the sticker assignment, some did not. In particular, 15% of individuals in the control group placed one or more stickers in their vehicle and 33% of individuals in the treatment group placed less than five stickers in their vehicle.
• Since the researchers tested all five stickers relative to a control group with no stickers, they were unable to comment on the efficacy of any individual sticker design. A later follow-up study with a larger sample found that sticker messages with only text and no images had no effect on insurance claims rates. Stickers with images of wrecked vehicles (event aversion theme) had the greatest effect at lowering claims, followed by stickers with images of riders shouting at the driver (supportive theme), and images of injured passengers (consequence aversion theme).
• When using entry into a lottery as an incentive, it is important to ensure that all individuals feel like they have a chance at winning. The researchers did this by dividing the 1000 matatus given stickers into groups of 200 and conducting the lottery for each group every fifth week. The follow-up study was also able to rule-out whether the lottery itself could have induced better driving of vehicles given stickers, through use of a “placebo” group of vehicles given a neutral sticker also able to participate in the lottery.
• See a review by GiveWell to learn more about the Zusha! Road Safety Campaign.