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.
Even the most advanced prototypes are having a hard time interpreting emergency sirens. If they are ever to be allowed onto real streets, autonomous cars will need to be able to respond appropriately if a police officer waves them down, or an ambulance tries to pass.
Most self-driving cars cannot yet reverse without human assistance, although this shouldn't be a problem to master, it's just not a priority for developers.
Quite how insurance will work remains unclear. The question of who pays out in the event of a crash involving a driverless car is still being debated and is seen as a major barrier to letting them loose on highways.
6. Public perception
If recent surveys are anything to go by, developers have failed at the first hurdle as it seems much of the public is actually too scared to even step foot in one of the cars. Half of Britons responded that they would be unwilling passengers in driverless cars over safety concerns, with 16 per cent professing to feel 'horrified' by the notion of unmanned vehicles driving on British roads. Four in ten would not trust an autonomous car to drive safely, believing it would jeopardise the welfare of drivers, cyclists and pedestrians, a survey from price comparison site uSwitch.com found.
If the autonomous car is to ever compete in the crowded automobile market, manufacturers will need to make sure the cost isn't prohibitive. Market researchers IHS Automotive forecast that the price for the self-driving technology will add between £4,500 and £7,000 to a car's price tag in 2025, a figure that will drop to around £3,000 in 2030 and about £2,000 in 2035, the year when the report says most self-driving vehicles will be operated completely independent from a human occupant's control.