What Are Lane Departure Warning Systems?

how lane departure warning systems work
Lane departure warning systems use sensors to make sure a vehicle stays inside its lane. ​

Lane departure warning systems are a group of safety technologies that are primarily designed to prevent high-speed accidents on highways and freeways. There are a few different types of lane departure warning systems, and some of them are more proactive than others. By warning the driver, or even taking automatic corrective actions, these systems are able to prevent many collisions and run-off-road accidents.

How Does Lane Departure Warning Work?

There are three primary types of lane departure warning technologies. While they all have the same general purpose, they achieve this goal in slightly different ways:

  1. Lane Departure Warning (LDW) - These systems represent the first iteration of lane departure warning technology, and they are the least invasive. When a vehicle equipped with this type of system drifts away from the center of its lane, the driver receives a warning. The driver is then responsible for taking corrective action.
  2. Lane Keeping Assist (LKA) - Also known as Lane-Keeping Systems (LKS) and by other similar names, this version of the technology goes one step further than the original LDW systems. When the vehicle drifts too far to one side or the other, and the driver doesn't take corrective action, the system will apply torque to the steering wheel. Unless the driver actively fights the system, this can effectively steer the vehicle back into the center of the lane.
  3. Lane Centering Assist (LCA) - This is the most invasive form of the technology. Rather than providing a warning, or kicking in only when the vehicle drifts toward the edge of its lane, this type of system is actually capable of keeping a vehicle centered in its lane at all times.
    how lane departure and keeping works
    Lane departure warning and keeping systems can provide alerts or take corrective action to keep a vehicle in its lane. Jeremy Laukkonen 

    Early lane departure warning systems typically used a single video camera to monitor lane markings, but modern systems can use visual, laser, or radar sensors.

    The methods that these systems use to provide corrective actions also differ from one situation to another.

    Some of the first lane-keeping systems made use of electronic stability control systems to keep a vehicle in its lane. This was accomplished by applying a slight braking pressure to the appropriate wheels. Modern systems are able to tap into power or electronic steering controls to actually provide a gentle steering correction.

    What’s the Point of Lane Departure Warning And Lane-Keeping Assist?

    According to the National Highway Transportation Administration, about 70 percent of all single-vehicle highway fatalities in the United States occur in run-off-road accidents. Since run-off-the-road accidents occur when a vehicle leaves its lane and drives off the roadway, lane departure warning systems have the potential to help prevent many fatal accidents.

    In theory, lane departure warning has a tremendous potential. In fact, AAA says that lane departure warning could totally eliminate almost 50 percent of all head-on collisions.

    The problem is that real-world test data hasn't lived up to that potential just yet. That could be due to the relatively few vehicles out there with lane departure warning in place, or there could be some other issue that hasn't yet become clear.

    How Do I Use a Lane Departure Warning System?

    If your vehicle has a lane departure or lane-keeping system, it’s a good idea to figure out which type you have. Since these two categories of lane departure systems offer different levels of protection, it’s important to know which one you’re dealing with. It’s also vital to understand the limitations of these systems.

    Vehicles that are equipped with an LDW system will issue a warning if your vehicle starts to drift out of its lane. If you’re familiar with the audible warning or looking for the visual cue on your dash, you’ll be able to take corrective action to prevent an accident.

    If your vehicle is equipped with Lane-Keeping Assist, you have an additional layer of protection. However, these systems are not an excuse for distracted driving. They are able to provide small amounts of corrective braking or steering, but it’s still vital to remain aware of your surroundings whenever you’re on the road.

    It might seem like a car equipped with LKA and adaptive cruise control can drive itself, but technology is still a poor substitute for an alert driver.

    Choosing a Lane Departure Warning System

    Since different automakers have different takes on lane departure warning and lane-keeping technologies, there are a lot of different options out there. So if you're in the market for a new car, and you do a lot of highway driving, it's important to take these systems into account.

    Here are some of the main features to look at when considering a vehicle that includes a lane departure warning system:

    • Audible warnings - Some systems provide an audible warning when the vehicle leaves the center of its lane. This is the least invasive type of warning.
    • Haptic feedback warnings - Some systems provide some type of haptic feedback as a warning. The steering wheel may vibrate, or the seat may vibrate. In many cases, the side of the steering wheel or seat that vibrates will indicate the direction in which you need to steer.
    • Visual warnings - Most systems also provide some type of warning indicator on the dash. This may be as simple as a warning light or as complex as a diagram that indicates which side of the lane you have drifted toward.
    • Automatic corrective steering - Some systems are capable of applying torque to the steering wheel to correct the position of the vehicle. When a vehicle has this feature, it's important to test drive and determine how much force is required to overcome this corrective action in case it happens at a bad time. If you feel too much force is applied, it may be a good idea to look at a different make or model.

      What Are the Limitations of Lane Departure Warning And Lane-Keeping Assist?

      Modern lane departure warning systems are more reliable than earlier iterations of the technology, but even the most advanced examples have limitations.

      These systems often rely on visual information to track the relative position of a vehicle within its lane, so anything that obscures the lane markers will render the technology useless. That means you usually can’t rely on your LDW or LKS in heavy rain, snow, or if there is excessive glare from the sun.

      Turn signals can also shut down your lane departure or lane-keeping system. These systems are all designed to shut off if a turn signal is activated, which prevents the technology from fighting you whenever you change lanes. If you accidentally leave your turn signal on after changing lanes, the system will remain dormant.