Google has applied for patents that could let its autonomous cars choose not to drive.

While Google engineers have claimed that they want to make a self-driving car so advanced it does not even need a steering wheel, a new patent under the heading ‘Engaging and Disengaging for Autonomous Driving’ describes a system that makes it harder to persuade a self-driving car to move.

The patent lays out a checklist that smart cars could follow before they engage autonomous driving.

First - checking if it is safe to switch modes. This includes measuring the distance to neighbouring or oncoming vehicles, checking whether the road is paved, smooth and wide enough for two cars to pass. It would also ascertain whether any manoeuvres are required at the time.

The last of these measures is designed to stop people from hitting the self-driving button when they are about to crash, which they may do to shift legal liability to the robot driver.

Second - Google is looking at making self-driving cars refuse to enter autonomous mode when the car is travelling out of its lane or over the speed limit, or possibly even when the road ahead is hilly or curved.

Thirdly - the cars will need to know their wider surroundings, and if they cannot determine their own location, are outside a well-mapped area, or be in an area where autonomous vehicles are forbidden to operate, the robot will not take over.

Additionally, “assessments may include… determining whether the current or future weather would make autonomous driving unsafe, uncomfortable for the vehicle’s passengers or damage the vehicle,” the patent states.

The cars will run self-diagnostics of their mechanical condition, checking that tyres are pumped to a certain pressure, oil levels are adequate, doors are closed and seatbelts are on.

“[The] computer may also use protocol data to assess the status of the vehicle driver. For example… using sensors or other methods to determine driver sleepiness, driver intoxication, or whether the driver is authorized or not to use the vehicle,” the documents state.

The Google patent says the cars could overcome some “preventive conditions” themselves, by recalibrating sensors, adjusting settings or waiting for weather and road conditions to change.

The engineers suggest listing tasks, one by one, on the instrument cluster until the car is ready drive itself, or the human driver decides to take the wheel themselves.