How Do Teslas Read Traffic Signals & Speed Limit Signs? (Explained)

One of the selling points of Tesla vehicles is that they are autonomous.

You can sit back and relax as the vehicle takes you to your destination.

But one question that remains is how they can read speed limit signs or detect traffic signals. After all, these are important aspects of maintaining safety and order on the road.

Here’s How Teslas Read Traffic Signals and Speed Limit Signs

Tesla vehicles have been equipped with a Traffic Light and Stop Sign Control feature that recognizes and responds to stop signs and traffic lights. It uses the car’s forward-facing camera and GPS data to slow down or stop the car when approaching traffic lights.

How Does the Traffic Light and Stop Sign Control Work?

When you enable Traffic Light and Stop Sign Control and are using Traffic-Aware Cruise Control or Autosteer, a message will pop up on the touchscreen display.

This is to inform you that an upcoming stop sign, traffic light, or road marking has been detected.

However, there has been instances where a Tesla wouldn’t stop automatically, and you cannot rely on the autopilot to do the job for you just yet.

As your car approaches the stop location, it will slow down and display a red line to show where it will stop. To keep going, you need to press the accelerator pedal briefly or the press stalk to permit the car to keep going.

Once you confirm you want to continue, the red stop line that had appeared on display will turn gray, and your vehicle will continue at your normal cruising speed.

With that said, there are times you’ll be approaching a green light, and there’s a car in front of you. If the vehicle proceeds through the intersection and your car detects that movement, it will also keep going without asking for your confirmation.

But this only happens when you aren’t in a turning lane, and the car detects your hands on the steering wheel.

There are times you can press the accelerator briefly or drive stalk to confirm you wish to proceed through the intersection.

But before you can enter the intersection, the light changes from green to yellow.

On such an occasion, the car will determine it isn’t right to proceed and stop.

Therefore, it’s your duty to press the accelerator to continue.

In terms of speed limit signs, Tesla uses a feature called ‘Speed Assist.

It uses the car’s camera to spot speed limit signs to enhance the accuracy of speed limit information on local roads.

The car will display the detected speed limit signs on the screen and use set the required speed limit warning.

Drivers can fine-tune this feature based on their preferences.

Under Which Conditions Does the Traffic Light and Stop Sign Control Operate?

Note that the Traffic Light and Stop Sign Control features has been designed to only operate under the following conditions:

  • The Traffic-Aware Cruise Control or the Autosteer features has to be engaged
  • The camera can detect a stop sign, upcoming traffic light, or a road marking. For instance, the cameras need to have a clear, unobstructed line of sight of the stop sign or traffic light.
  • The touchscreen displays the traffic lights in a bold format. For instance, model Y will not acknowledge a traffic light on the screen if it appears as faded.

Traffic lights that aren’t directly ahead of the camera appear as faded. Let’s say a traffic light is on an adjacent lane. The screen will show it as faded, and hence the car will neither slow down nor stop.

What Are the Limitations of the Traffic Light and Stop Sign Control?

Despite this feature’s many possibilities, it has several limitations.

Your car may not stop at:

  • Toll booths
  • Crosswalk systems
  • Railroad crossings
  • Keep-out cones
  • Roundabouts
  • Temporary traffic lights,
  • yield signs,
  • and certain stop signs like those at a construction site

Aside from that, this feature may fail to operate as it should, disengage or completely fail to operate in the following conditions.

· A stop sign, road marking, or traffic light that’s obstructed by a large vehicle or tree

· A camera that is damaged, obstructed, covered, or not calibrated properly

· Poor visibility caused by snow, fog, and heavy rain. They will obstruct the camera’s view

· Driving on a road with sharp curves or on a hill whereby the cameras can’t see upcoming stop signs and traffic lights.

How Do Teslas Know When Traffic Lights Turn Green or Red?

Tesla vehicles have cameras around the car connected to a computer system based on artificial intelligence (AI) technology.

The AI software has been trained to recognize the shape and color of traffic lights to allow the vehicle to behave accordingly.

In addition, expect fewer embarrassing moments at the intersection. The car produces a chiming sound that alerts you when the traffic light turns green.

It’s a great feature considering that most people can get distracted by other things while waiting for the ‘go‘ signal.

The chime lets you know it’s time to move. If there’s another vehicle in front of you, the chime won’t go off until it moves.

How Can Teslas Register the Speed Limit on Signs?

Initially, Tesla vehicles relied on GPS data to detect speed limits.

But this came with a lot of inaccuracies, and some people got tickets for not sticking to the required speed limits.

Fortunately, the company released new software that uses the car’s camera to spot speed limit signs. You should be able to stick to the required limit accurately without worrying that you’ll get a ticket because your vehicle sped up prematurely.

What Traffic Signs Do Teslas Understand?

Tesla vehicles can detect red, yellow, and green traffic lights, which mean stop, go and slow down, respectively.

How Well Does Teslas Autopilot Work With Traffic Signs?

The autopilot feature depends on whether your cameras and sensors are reliable.

There have been problems reported with the sensors on Model S which are important to be aware of in order to not trust the driving assisting features too much.

However, the sensors are great when it comes to stuff like parking your Tesla.

If they can clearly detect traffic signs, then they’ll assist for a better driving experience.

What Happens if the Cameras and Sensors Get Dirty?

Dirty cameras and sensors affect the autopilot performance.

Your car depends on these devices to detect traffic lights, speed limits, and road markings.

To ensure your cameras capture a clear picture and record accurate information, keep the sensors and cameras clean from obstructions.

Also, environmental factors like fog and rain can prevent the cameras and sensors from working correctly.

In this case, there isn’t much you can do about it apart from ensuring you’re in complete control of the vehicle to avoid breaking any traffic rules.

How Often Do Teslas Misinterpret Traffic Signs?

It’s not uncommon for Tesla vehicles to misinterpret traffic signs.

In one study, researchers found that the cameras could be tricked into misreading a 35 MPH sign as 85 MPH.

They did this by partially obstructing the 3 in a way that a person driving a normal vehicle wouldn’t even notice that the ‘3’ had been obscured.

In another instance, the car mistook the moon for a yellow sign and slowed down. However, this was only reported by one user, but it only shows that the car can misread traffic signs at times.

How Precise Are the Sensors on a Tesla?

Tesla sensors are pretty accurate. Most people have done this practically and gotten accurate results.

If the sensor tells you an object is about 12 inches away, then there is a high chance the object is that far away. And if not, it can be more or less by one or two inches only.


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