The New Yorker's Jon Lee Anderson ("Gangland: Who controls the streets of Rio de Janeiro?") reports that Rio is "the top-ranked in the world for 'violent intentional deaths.'"
How will that work for the 2016 Olympics? Beijing got mixed results with efforts to dampen air quality problems. Los Angeles got better results with auto traffic in 1984. But in the first days of the '84 Olympics, an unexpected boost came from the locals staying away or staying home.
It's doubtful that Rio's gangs will also stay home. But the real point is that Olympic games are interludes. LA's road conditions are now about the same as in 1984, no better and no worse. Whatever LA or Beijing authorities did for the two weeks of the games, they could not duplicate it after the closing ceremonies.
But we all grasp for interludes. Look at the footage of cheering Brazilians.