The US Department Of State
has this to say:
....... the country has a high crime rate. Numerous U.S.- citizen residents and visitors have been victims of violent crime in recent years, and they have sometimes suffered severe injuries. Carjackings, armed robberies, and stoning of vehicles are problems in Port Moresby, Lae and Mount Hagen. Pickpockets and bag-snatchers frequent crowded public areas.
Hiking in rural areas and visiting isolated public sites such as parks, golf courses, beaches, or cemeteries can be dangerous. Individuals traveling alone are at greater risk of robbery or gang rape than those who are part of an organized tour or under escort. Visitors to Papua New Guinea should avoid using taxis or buses, known as Public Motor Vehicles (PMV's), and should instead rely on their sponsor or hotel to arrange for taxi service or a rental car.
Road travel outside of major towns can be hazardous because criminals set up roadblocks near bridges, curves in the road or other features that restrict vehicle speed and mobility. Visitors should consult with the U.S. Embassy or with local law enforcement officials concerning security conditions before driving between towns.