For drivers in Mexico, the rule of thumb for traffic accidents is simple: el que pega, paga! In other words, the perpetrator of a crash — i.e. the incoming vehicle — pays.

In a country where many are uninsured, that kind of unspoken understanding makes sense. But the pega-paga approach has also created an opportunity for scammers to pocket some ill-gained pesos through a practice known as montachoques, the operative word being choque, Spanish for "crash."

An extortion technique being used increasingly in Mexico City, it involves provoking an accident by halting a car on a busy highway, then demanding compensation from the person who crashed in from behind. When victims are reluctant to pay, they are threatened and sometimes even attacked, a senior police official in the eastern sector of the city recently told the Milenio newspaper.

The official, Luis Martínez Rodríguez, described a typical maneuver as overtaking a car, then suddenly slamming the breaks to provoke a crash. The "injured party" then steps out, sometimes with companions, and demands compensation, with sums ranging from the equivalent of around $70 euros to $1,500.

Two or even three cars may be involved to ensure the victim is trapped into the situation. In one case the driver filmed the "repeated crashes' into his car, calling it an "attempted homicide." Police have identified the city's main ring roads as a choice location for this crime, usually undertaken outside rush hours, to allow maneuvering.