The road between Tingo Maria and Pucallpa is infamous for robberies. Particularly buses are prone to suffer, as some of the robbers get on as paying passengers and then stop the bus while more robbers get on and strip the passengers of all valuables. It is much safer to use a plane from Lima. If you have to use the road, try organizing a taxi or lorry from Huanuco. Avoid travelling when there are special events in Pucallpa or Christmastime, as the robbers are known to be more active then. And don't ever travel this road at night. Pucallpa is particularly dangerous around Christmastime. Many robberies occur during December, and police corruption is at its worst then, too. The situation seems to have improved since the road between Tingo Maria and Pucallpa is mostly paved now as of 2011.
