What is Traffic Jam Assist?

Jessica Shea Choksey | Jul 09, 2021

Along with death and taxes, traffic is one of life’s inevitabilities. It is also a source of daily stress for millions of Americans who drive to and from work every day. To help mitigate some of the fatigue associated with stop-and-go commuting, a growing number of automakers offer Traffic Jam Assist (TJA). This Level 2 advanced driving assistance system (ADAS) combines adaptive cruise control and lane-centering capabilities to ease the burden of getting through clogged highways and traffic congestion.

Volkswagen Traffic Jam Assist Illustration

How does TJA work? - Find the best car deals!

To help make heavy traffic more bearable, TJA essentially acts as a low-speed version of adaptive cruise control. It utilizes a front-mounted radar unit, cameras, and sensors to detect vehicles ahead and automatically adjust to their speeds. But as opposed to adaptive cruise control’s goal of maintaining highway cruising velocity, TJA takes effect when a car approaches slowed traffic and slows to a crawl.

Designed to operate at speeds under 40 miles per hour, TJA will adjust the vehicle’s following distance based on the stop-and-go traffic ahead. In other words, the driver does not have to operate the gas or brake pedals through heavy traffic actively. The TJA system will accelerate and decelerate the vehicle on its own without driver intervention.

TJA will also bring the vehicle to a complete stop and then resume driving when the traffic ahead moves. However, most TJA systems require that the driver re-engage the system with a light touch to the gas pedal if the car has been completely still for more than 30 seconds. This “reawakening” of the system helps ensure the driver is paying attention to the overall traffic conditions and not simply tuning out because the car has been resting for an extended time. In the same vein, most TJA systems disengage if the driver’s hands leave the wheel for too long.

In addition to managing speed, most TJA systems also utilize lane-centering technology to keep the vehicle from drifting. The system uses a camera to identify lane markings on the road surface and automatically provides subtle steering inputs and minor corrections to keep the car in the center of its lane. This functionality helps drivers who may lose alertness and begin drifting after long periods of slow-moving traffic.

A driver can make an intended lane change at any time while using TJA with regular steering input. This action will override the TJA system’s lane-centering functionality. Once the vehicle has made the lane change, the system will resume lane-centering by tracking the markings of the new lane. Some TJA systems may require re-engagement after the driver has taken control of the steering. All TJA systems allow for full driver override at any time in the event of an emergency.

Although TJA has many benefits, similar but more sophisticated systems exist, such as Hyundai Motor Group’s Highway Driving Assist (HDA) and Highway Driving Assist II (HDA2). These systems give HyundaiGenesis, and Kia models a definitive edge over vehicles with TJA alone, employing navigation-based guidance.

Beyond HDA, automakers such as Audi and Honda, among others, are currently developing the next generation of TJA, which would arrive as a Level 3 autonomous vehicle system in the foreseeable future. With this technology, drivers will enjoy higher levels of safety, security, and stress reduction while traversing traffic on congested highways in a potentially hands-free manner.

Warnings and Watchouts - Find the best car deals!

Although TJA is a semi-autonomous feature in low-speed driving conditions, it requires driver alertness for safe and effective operation. The driver should keep their hands on the wheel to maintain a proper course. Notably, TJA is for use on highways only, not in-town driving where stoplights and stop signs are commonplace. As such, TJA should be off when not in use so it does not disrupt low-speed driving operation in non-highway situations. In general, TJA should not be used when any of the following conditions are present:

  • Inclement weather (rain, snow, fog) that impedes TJA’s ability to identify objects and road markings
  • Roads with sharp curves
  • Highway interchanges (entry and exit)
  • Slippery surfaces such as icy or snow-covered roads
  • Long, descending slopes
  • Two-wheeled vehicles directly ahead
  • Tires of different sizes are in use (a temporary spare tire)
  • Tires with insufficient tread are in use
  • A towing maneuver of any kind is in progress (camper, boat trailer, etc.)
  • Roads without white or yellow lane lines or markings

Drivers should be aware of the surrounding conditions and always keep a safe distance from vehicles ahead.

Summary - Find the best car deals!

Traffic Jam Assist is an ADAS that not only supports safer, stress-free driving but can serve as a steppingstone for automakers to reach their autonomous mobility goals. You can learn more about modern vehicle technologies in the Shopping Guides section of JDPower.com.

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