How do self driving cars work?

Find out how driverless cars work by using the technology in cars that are on sale today

By BuyaCar team

The day driverless cars become the norm on public roads is still a fair way off, but the technology is already being actively tested by the likes of Tesla and Google. The idea behind electric cars is that we, with our busy lives, will be able to travel in comfort while also being able to work, eat and sleep in our own private space.

A move towards autonomous driving has already begun. Technology we've been making use of for years, such as ABS (anti-locking brakes) and cruise control, are very primitive versions of the type of tech that driverless cars will one day rely on.

There are cars on sale today that can park themselves, change lanes on the motorway, and manage the distance between you and the car in front without any input from the driver, thanks to technologies known as park assist, lane keeping assist and adaptive cruise control respectively.

These are the beginnings of driverless car technology. It’s not perfect and early prototypes can still be caught out by simple situations, as well as poor road surfaces and unclear road markings, so they still need monitoring by a driver in their current guise. Autonomous driving tech is gradually being improved, though, and manufacturers are confident that with time it will be safe and entirely normal to pack your children off to school in a driverless car - letting it tackle the school gate scrum while you head off to work in the other direction.

How driverless cars can see

Like a human, self-driving cars need eyes, ears and a brain to do their job. Several types of sensors act as eyes and ears, while powerful computer processors replace the brain, interpreting the data.

Radar sensors

These are located around the car and monitor the location of obstacles and other vehicles. They are good at detecting obstacles several hundred metres away.

Lidar sensors (Light Detection and Ranging) sensors

These sensors project beams of laser light that measure the car’s distance from surrounding objects including kerbs and approaching vehicles. They can even identify road markings.

Video cameras

These interpret traffic signs, and monitor the surrounding area checking for pedestrians, vehicles and other hazards.

Ultrasonic sensors

These emit high-frequency signals that can detect nearby objects extremely precisely: vital for low-speed manoeuvring.

Vehicle sensors

From the speed that the wheels are turning to the position of the driver’s hands on the steering wheel, dozens of onboard sensors monitor how the vehicle and driver are behaving.

Electronic control unit (ECU)

ECU is the name used by the car industry for the computers installed in vehicles. They receive the data from the sensors, analyse it and calculate what the car needs to do, which could involve steering, accelerating or slamming on the brakes.

How driverless cars work at the moment

Combine all of the self-driving features - as you can do in cars such as the Tesla Model S, Mercedes E-Class and 2017 BMW 5 Series - and you have a car that can - in theory - handle the majority of a long-distance commute, although the technology is still at a stage where it needs constant human supervision.

Active city stop

This technology uses Lidar to detect objects in front of the car, and constantly calculates the force required to stop the vehicle in time to avoid hitting them. If it calculates that a collision is imminent, it will close the throttle and activate the brakes. It is operable up to 30mph and has been shown to dramatically reduce the incidence of forward collisions. As a result, the insurance industry views cars fitted with the system much more favourably.

Active park assist

This system uses ultrasonic sensors to guide the car into a parking space. The driver approaches their chosen space and alerts the car to it by operating the indicator stalk. They drive forward a little then stop, engage reverse and the car performs the parking manoeuvre, aided by small throttle and brake inputs from the driver.

Adaptive cruise control

This enables a car to keep a pre-set distance from the vehicle in front when cruise control is activated. A forward-mounted radar monitors the distance separating the vehicles and the ECU issues throttle commands to maintain the gap set by the driver.

Blind spot information system with cross-traffic alert

Radar mounted on the rear corners of the car that scan the rear and sides of the vehicle detect vehicles approaching from behind that would otherwise fall into the driver’s blind spot. When a vehicle is detected, the system displays a warning sign in the car’s wing mirror. When reversing out of a parking space, the same sensors detect vehicles approaching from the side.

Cornering control

If this system detects that the car is entering a corner too quickly, it applies the brakes and backs off the throttle to help bring the car back into line.

Driver alert system

There are many variations on this system, some taking data from the throttle as well as the steering system. A typical system uses a forward-facing video camera, mounted in front of the rear view mirror, that monitors the car’s position relative to lane markings. The system also monitors the driver’s steering inputs. If it detects the vehicle is ‘wandering’ it will issue a warning and display a message advising the driver to take a rest.

Forward collision with brake support

This system uses a forward mounted radar to monitor the distance between it and the car ahead. If it calculates a collision is imminent, it sounds a warning to the driver, while also pre-boosting and tuning the brakes for a quicker and stronger response.

Hill start assist

This system automatically applies and releases the car’s brakes when it detects the vehicle is parked on an incline, and as the driver presses the accelerator pedal to pull away.

Intelligent lighting

Headlights that can ‘swivel’ to illuminate corners, dip automatically if they detect a vehicle ahead either in the same lane or approaching and adjust the range of the dipped beam are all available, using the car's cameras to detect other traffic

Intelligent speed assist

This technology allows the driver to set a speed limit that only a determined push on the accelerator pedal can overcome. When the car’s forward-facing camera detects the car has entered, say, a 30mph speed restriction, the technology activates the speed limiter.

Lane-keeping system

Using a forward-facing video camera, typically mounted in front of the rear view mirror, this system monitors lane lines to check the car is holding position. When it detects the vehicle is about to leave the lane it ‘pulses’ the steering wheel to alert the driver. More advanced systems can gently take control of the steering wheel to guide the vehicle back into the lane. However, the driver can overrule it with additional force.

Pre-collision assist with pedestrian detection

This system uses radar and video cameras to scan the area around the car for vehicles and pedestrians. If it detects a collision is imminent, it can apply the car’s brakes with full force. It can help reduce the severity of rear and front collisions, as well as avoid them altogether.

Traffic sign recognition

A forward-facing camera on the car detects speed limit signs. The system then reminds the driver they have entered a restricted speed zone by displaying the limit on a head-up display or in the car’s instrument cluster. An alarm is sounded if the car exceeds the limit.

Mercedes’ driverless car

Mercedes is one of several car makers offering advanced semi-autonomous features in its latest cars. For example, the new E-Class, launched in 2016, is available with what the company calls a Driver Assistance package. At all times, the driver’s hands must be on the steering wheel. If a manoeuvre has been activated but the driver removes their hands from the wheel, the car comes to a controlled stop.

The Driver Assistance package includes:

Drive Pilot

This uses a stereo camera and radar to enable the car to follow the road or the vehicle ahead, keeping the vehicle in its lane and maintaining a pre-set distance.

Speed limit pilot

A camera detects the sped limits on traffic signs which are then automatically adopted by the cruise control.

Active lane change assist

If the driver uses the indicator to signal that they wish to change lanes, the radar and other sensors check the way is clear to overtake. If it is not, the vehicle does not perform the lane change. However, if it is clear, the system performs the lane change with a smooth steering effort.

Meanwhile, Mercedes has been granted a licence to test fully autonomous cars in Nevada, in the US.

Advanced features under development include:

Steering pilot

This enables the car to automatically decelerate for gentle as well as sharp corners, while driving autonomously.

Junction pilot

The car can automatically decelerate and come to a standstill at junctions, when these are plotted in the vehicle’s sat-nav map data.