Parking sensors are devices that we use every day. But how do parking sensors work? And what other systems are active every time you choose Reverse? We’ll find out.
It’s something you take for granted. Every time you get in the car, shift into reverse, and come back out of the driveway, there are a variety of systems in place to ensure you don’t reverse into anything or anyone.
These systems are designed to enable forward and reverse parking and to keep an eye on cross traffic when reversing. There are even systems that remember your most recent steering inputs to make it easier to reverse out of tight spaces.
We wanted to make a video that explains how the main parking systems used in cars today work. While there are small differences between the cars on the market, most parking systems use the same core equipment as a base – these are ultrasonic or electromagnetic parking sensors, radar and cameras.
In order to cover the entire range of parking technologies, we use the Kia Sorento GT-Line and the BMW X5. These two cars have technology that covers everything from reverse parking to remote parking.
How do ultrasonic parking sensors work?
Most new cars on the market today are equipped with a combination of ultrasonic front, rear and side parking sensors.
You can tell if these are attached to your car by looking for small circles built into your front, rear, or side bumpers.
They are usually body colored, but they can be a different color and are usually evenly spaced from one another.
Ultrasonic parking sensors emit a high-frequency sound wave (a frequency so high that the human ear cannot hear it) that hits an object and is then reflected back to the car. The time it takes for the sound wave to return to the car is then used to calculate the distance between the parking sensor and the object.
For all of the tech nerds out there, the formula is distance = 0.5 * time * speed of sound. Since the speed of sound varies based on temperature and humidity, the car has a built-in temperature sensor that varies the speed of sound calculation to ensure precision when parking.
However, ultrasonic parking sensors have some disadvantages. Sound waves are absorbed by things like clothing and human flesh. Sound waves can also be deflected in other directions by metal rods with a circular area.
Because of this, cars use multiple parking sensors. They are used for redundancy and confirmation of distances in the event that sound waves are deflected or absorbed by some objects.
Ultrasonic parking sensors only have an effective range of approx. 3-5 m, which makes them ineffective for detecting greater distances.
How do electromagnetic parking sensors work?
Similar to ultrasonic parking sensors, electromagnetic parking sensors send out a wave and then control its return. There are a few key differences, however.
Visually, you will not recognize electromagnetic parking sensors as they are generally placed behind the bumper and are not visible. They come in the form of a plastic strip with glue and are the most common in the aftermarket.
Instead of sending out a sound wave, electromagnetic sensors send out a radio wave. The radio wave bounces off an object and then returns to the sensor. The frequency change is used to calculate the distance from the sensor to the object.
While electromagnetic sensors offer a larger detection field compared to ultrasonic sensors, they are affected by the fact that they only detect objects when the car is moving.
This means that if an object moves between your car, comes to a standstill, and then starts moving again, you can face disruptions and inaccuracies.
How does a 360 degree or bird’s eye view work?
Parking sensors are useful, but using sensors as the only parking method may not always be effective.
Getting a visual indication of the space around the car will help you see what the parking sensors may have missed.
We’ve seen reversing cameras that are commonly used in new cars, but car brands have pushed this further by adding additional cameras to the mix.
The 360 degree camera (also known as a bird’s eye view camera) uses cameras attached to the back, sides, and front of a vehicle to stitch together an image that is a view from the top of the vehicle looking down seems to offer.
Instead of using cameras above the vehicle, the car uses ultra-wide angle cameras and the image from each camera is stitched together to create an illusion of a bird’s eye view above the vehicle.
The quality of these cameras is very different in the different segments. Some are high quality and add value while others are low quality and quite grainy, making them difficult to use and effectively pointless.
In some vehicles, these cameras are automatically activated at low speeds when they approach objects to make parking easier.
How does the rear cross traffic alarm work?
Rear Cross Traffic Alert is technology that can alert the driver, and in some cases even brake the vehicle, in the event that an approaching vehicle, cyclist or pedestrian may collide with the vehicle as it continues to reverse.
The same technology is also applied to the front of some cars and warns and brakes when the vehicle leaves a parking lot in oncoming traffic.
We know that ultrasonic parking sensors only have an effective range of 3 to 5 meters. Therefore, vehicles with this technology use radar to detect vehicles.
Radars are mounted on the corners of the rear bumper (and on the corners of the front bumpers in vehicles with forward-facing versions of this technology) and angled to point towards vertical traffic.
In a process similar to electromagnetic parking sensors, a radio wave with a certain frequency is emitted before it returns to the vehicle. Once it returns, the frequency change is measured to determine the distance.
If a cyclist, vehicle or pedestrian approaches the rear of the vehicle while reversing, the radar detects the change in the reduction in distance, informs the driver with a warning and then continues to brake if a collision is imminent.
Other parking technologies
There are other parking technologies that you may have heard of derived from the technologies discussed above. Each of these systems use one or more of the technologies to create new derivatives of parking technologies that help drivers every day.
Remote parking technology
Tesla was one of the first manufacturers to introduce a remote parking feature from the Summon brand. With Summon, the driver can move the vehicle forwards and backwards from outside the vehicle.
This technology has evolved through other brands where a vehicle can be moved from the outside with the key, and Tesla recently developed it further with Smart Summon, which allows the vehicle to drive autonomously to the driver in a parking lot.
Depending on the vehicle, the car uses a mixture of parking sensors, radar and camera technology to move the vehicle in the direction instructed by the driver.
A signal from the driver steers the vehicle, stops and starts the movement. The key (or your phone) acts as a dead man’s switch and instantly stops the car when the button is released.
Autonomous emergency braking is common on most new cars these days and stops the vehicle if a crash is imminent and the driver has not responded.
Reverse AEB uses ultrasonic parking sensors to detect objects at the rear of the vehicle. If the driver does not stop and a crash is imminent, the car suddenly brakes to prevent a crash.
As with all of these systems, there are restrictions on how they work and the driver must always ensure that he is monitoring the space behind the vehicle.
Autonomous parallel and vertical parking
Semi-autonomous parallel and vertical parking uses a mix of ultrasonic parking sensors and electric motor-powered steering to steer a vehicle into a parking space.
Algorithms in the vehicle’s ECU measure the size of the parking space either constantly or when necessary to determine whether the parking space suits your vehicle. When your vehicle determines, based on a set set of dimensions, that it will fit in the bay, it will display that information to the driver and wait for a command to begin the process.
As soon as the process begins, the vehicle begins reversing into the park (either parallel or perpendicular) and moves the steering wheel independently. This system only works on vehicles with electrically assisted racks and not on vehicles with an older hydraulic type.
During the process, the driver remains near the brake pedal ready to stop the car if the process does not work properly.
Some cars, like the BMW X5, actually shift gears too, so the driver just has to be careful.
Some vehicles also offer the option of getting assistance leaving a park. Once the vehicle is parked, a push of the right button begins the process of rocking the car with sufficient steering lock to exit the park.
It works the same way as when entering the park. Due to the given steering geometry and the given distance between the vehicles, the vehicle’s control unit can calculate the correct steering movements in order to maneuver out of a parking space.
The last technology we’ll cover is the BMW Reverse Assistant. While it’s currently only available for BMWs, we suspect this will be introduced by other brands at some point.
BMWs with this technology remember the last 50 m steering input and allow the driver to recycle this steering input backwards.
What’s the point of that? If you find yourself on a narrow one-way street and find that you need to reverse, you can do so by pressing the Reverse Assistant button. You no longer have to go without curbs and other cars when driving backwards.
It uses a mix of the parking sensor technology listed above and the steering input memory to reproduce the last 50m of steering inputs.