1. Mapping
Every street, pavement and driveway that will be used by a self-driving will need to be mapped. To give a sense of scale of the project, there are four million roads in the US alone. However, Google is used to large-scale mapping projects, and Google Street View has helpfully already laid down some of the groundwork. Chris Urmson, head of Google's self-driving project, says researchers "don't see any particular roadblocks" to accomplishing it.
2. Weather conditions
Little testing has been done outside the temperate Californian climate. The danger is the cameras and lasers will have a hard time dealing with challenging weather conditions such as thick fog, heavy rain and snow.