Out of the 1.3 million road deaths that occur each year, roughly 90% occur in the developing world.

A growing body of research suggests those rates might fall if people complained more.

Over the last eight years, Georgetown University researchers have found one of the cheapest, most effective ways to minimise the number of traffic fatalities in Kenya is to place stickers inside matatus, or minibus taxis, that encourage passengers to speak up if their driver is being unsafe.

Drivers, meanwhile, are incentivized to place the stickers in their buses because it grants them entry into a weekly lottery for cash prizes.

One study in 2010 of 2,500 matatus and another in 2015 of 12,000 matatus found that evocative stickers led to fewer deaths and insurance claims. Drivers also reduced their average speed if their buses carried stickers warning passengers of speeding, the research found.

Researchers estimate the program prevented 140 accidents and 55 deaths per year.

The stickers came courtesy of the charity Zusha!, which aims to reduce traffic fatalities in east Africa — primarily Kenya, Tanzania, and Uganda.

GiveWell, a nonprofit that analyses charities for their effectiveness, recently announced it was considering including Zusha! (Swahili for “protest”) on its upcoming list of top charities of 2017, due out in November.

GiveWell points to some compelling data from the randomised trials — namely, that something as small as a sticker cut collision rates by up to two thirds in the pilot study and up to one third in the larger follow-up study, just due to people feeling comfortable complaining.

“These effects seem surprisingly large to us, and we are interested to see whether the intervention will find similar effects in future [randomised controlled trials],” GiveWell wrote on its blog in February.

Behavioural economists call interventions like Zusha!’s stickers a “nudge.” Nudges are small, environmental changes that subtly push (or nudge) people toward some healthier, safer, or more financially lucrative behaviour over a more destructive one.

One of the most famous examples of a nudge in action involves organ donation. Countries whose organ donation forms make becoming an organ donor the default option, opposed to a box people need to actively check, see considerably more people sign up.

The nudge exploits people’s unwillingness to lose what they already have, which economists call “loss aversion.”

Researchers have fond the matatu stickers seem to work because people need the nudge to vocalize their concerns. Though it might seem trivial, even something as cheap as a sticker is enough to grant that life-saving permission.

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