A US patent for self-driving cars has been awarded to Google. The intellectual property rights relate to a method to switch a vehicle from a human-controlled mode into the state where it takes charge of the wheel. It explains how the car would know when to take control, where it is located and which direction to drive in.

The search firm suggests the technology could be used to offer tours of tourist locations or to send faulty models to repair shops. The application for Transitioning a Mixed-mode Vehicle to Autonomous Mode was applied for in May, but had been hidden from public view until this week.The document describes using two sets of sensors. The first identifies a "landing strip" when the vehicle stops. This then triggers the second set which receives data informing the machine where it is positioned and where it should go.

"The landing strip allows a human driving the vehicle to know acceptable parking places for the vehicle," the patent filing says. "Additionally, the landing strip may indicate to the vehicle that it is parked in a region where it may transition into autonomous mode."Direct and drive

Google says the landing strip could simply be a mark on the ground, a sign on a wall, or lines or arrows showing where the vehicle should be parked. To detect which landing strip it has been parked at, the document says the car could activate a GPS (global positioning system) receiver to find its rough location and then use its sensors to detect trees, foliage or other known landmarks to determine its exact position.