THE unofficial motto of the Democratic Republic of Congo was first uttered six decades ago by Albert Kalonji, the leader of the short-lived secessionist state of South Kasai: “This is your home, fend for yourselves.” With hardly any formal economy in Congo, let alone a welfare state, people do whatever they can to get by. Ordinary folk farm, trade, smuggle and hustle. Officials and rebels loot and extort. Congolese joke that “fend for yourself” is Article 15 of the constitution.

The real Article 15, adopted in 2006, urges the state to stamp out sexual violence. For some reason, the police seem to put more effort into upholding the mythical Article 15. A new study by Raul Sanchez de la Sierra of Harvard and Kristof Titeca of the University of Antwerp found that in Kinshasa, the capital, traffic cops receive about 80% of their income from “informal tolls”.

Every driver in charge of a spluttering yellow taxi or battered local bus (nicknamed “spirits of death” for their shoddy maintenance) must pay a “protection fee” to traffic officers. This is done by sticking a fist out of the window at certain junctions on the boulevard and dropping a note worth $0.30 into a waiting policeman’s hand. If this money is not paid, the officers will find ways in which the vehicle is breaching the law and impose a large fine. “Most cars tend to have some kind of infraction. If not, [the cops] will make something up,” Mr Titeca says. “I was once stopped because the policeman said the taxi driver needed a licence to carry a white person.”

To maintain a lucrative position on the boulevard a police officer must “thank” the superior who put him there. Each day he will have to arrest a pre-negotiated number of drivers and escort them to the police station, where his superior will demand a bigger backhander for himself. (Occasionally motorists are made to pay legitimate fines, too.) If an officer fails to meet the quota, his boss may withhold the orange waistcoat that all traffic policemen have to wear.

For Kinshasa’s weary drivers, dealing with the police requires charm, negotiation skills and unflappability. When your correspondent was taking a taxi in Kinshasa, a drunk policeman half launched himself through the window to demand money. The driver simply laughed. Once the officer had retreated just enough, he sped off.