This is another Guatemala City idea that I found interesting. The regular city buses are like what you find in Nicaragua -- mostly old, willing to stop anywhere and a better than average place for criminals. What Guatemala City did was create a separate fleet of buses -- green because that is their color contrasting with the red regular buses.
The buses only travel specific routes and only stop in stations such as the one in the photo. The stations are at the level of the bus floor so the doors are not suited for non-station use. The stations are similar to subway stations in New York and such were you pay with a token to pass through a turnstile. Thus there is no cash changing hands on the bus.
As there are a limited number of places where the doors get opened it is much easier to patrol the bus routes.