NAIROBI, Kenya — Clutching the door frame, Sheriff Safania Maina leans out of the bus as it hits potholes going 45 miles per hour. He jumps out of the door of the vehicle as it slows down. He starts to run alongside it. He yells, encouraging people to board . He spots a prospective passenger and bangs on the side of the vehicle to signal the driver to stop. He helps a woman with her bag get on. He hops back in.

“This is my office,” he yells, as “Humble” by Kendrick Lamar blares out of bus’s 28 speakers.

Mr. Maina is one of many young people in Nairobi who work on a matatu, the privately owned buses that have transported at least 60 percent of Nairobi’s population since the early ’60s. The word matatu comes from the Kikuyu word for “three,” referring to the three ten-cent coins used to pay for a ride to the city when matatus first started operating. In the mid-to late 1990s, matatu drivers became known in Nairobi for their infamously dangerous driving habits, and the industry was linked with violent criminal gangs like Mungiki, who infiltrated matatu routes and extorted “protection” money from matatu crews.