Adaptive Cruise Control: What You’re Not Allowed to Do

You’re not allowed to treat adaptive cruise control (ACC) as self-driving. You must remain attentive, keep hands on the wheel, obey speed limits, and avoid using ACC in unsuitable conditions such as heavy rain, snow, or dense urban traffic. You also may not text, read, sleep, or rely on ACC to detect stationary objects, and you must not obstruct its sensors. Below is a detailed breakdown of the limits and responsibilities that apply to ACC in modern vehicles.

What ACC Does—and Doesn’t Do

ACC is a driver-assistance feature (SAE Level 1) that automatically manages your speed and following distance to a vehicle ahead. It does not steer (unless paired with a separate lane-centering feature), does not make decisions at intersections, and is not designed to identify every stationary or cross-traffic hazard. The driver remains legally and practically responsible for vehicle control at all times.

Common Prohibitions and Misuses

The following points summarize behaviors and uses that are prohibited by law in many jurisdictions or explicitly warned against by automakers and safety regulators when operating ACC.

• Do not treat ACC as autonomous driving: you may not sleep, read, or divert attention from the road.
• Do not take your hands off the wheel or your eyes off the road; ACC is not a hands-free system unless your vehicle specifically supports and authorizes hands-free driving under defined conditions (ACC alone does not).
• Do not use a phone or engage in other distracted-driving activities; distracted driving laws still apply.
• Do not exceed posted speed limits; ACC does not legalize speeding, even if it allows you to set higher speeds.
• Do not assume ACC will detect or stop for stationary objects at highway speeds (e.g., stopped vehicles, road debris, or end-of-queue traffic); many systems are not designed to consistently do so.
• Do not set dangerously short following gaps; you are responsible for maintaining a safe, legal distance.
• Do not block, cover, or modify sensors/cameras (e.g., with aftermarket accessories, paint, vinyl wraps, or dirt/ice) or ignore sensor warnings/malfunctions.
• Do not rely on ACC to handle cut-ins, merges, or complex traffic patterns without driver intervention.
• Do not use ACC if warning lights are illuminated or the system reports limited functionality.
• Do not assume ACC will comply with variable speed limits or temporary work-zone limits unless your car specifically integrates that capability and you confirm it’s active and accurate.

These restrictions exist because ACC supports longitudinal control only and relies on sensors that have known limitations; ultimate responsibility remains with the driver.

Situations Where You Should Not Engage ACC

Automaker manuals and safety agencies advise against using ACC in several road and weather scenarios where sensor performance and stopping margins may be impaired.

• Severe weather: heavy rain, snow, sleet, ice, fog, or glare that reduces visibility or traction.
• Winding, hilly, or unpaved/gravel roads where speeds vary rapidly and traction is uneven.
• Construction zones, school zones, or areas with complex traffic control and frequent speed changes.
• Urban streets with pedestrians, cyclists, frequent intersections, and parked vehicles.
• Heavy, unpredictable stop-and-go traffic unless your vehicle supports stop-and-go ACC and you remain fully attentive.
• Towing or carrying unusual loads if your owner’s manual advises against ACC use in those conditions.
• Poorly marked or degraded road environments where sensor performance may be compromised.

In these settings, driver judgment and continuous manual control generally offer better safety margins than ACC’s automated gap-keeping.

Legal and Warranty Considerations

Most jurisdictions require a human driver to remain in control and attentive at all times when ACC is engaged. Using ACC while distracted, impaired, or asleep can violate traffic laws and lead to criminal liability in a crash.

Tampering with or obstructing sensors may void warranties and degrade safety performance. Following too closely or speeding—even with ACC active—remains enforceable as a violation. Always verify region-specific rules and your vehicle’s manual for system-specific constraints.

Best Practices Instead

If you choose to use ACC, adhere to these practices to keep its benefits without compromising safety or legality.

• Stay engaged: hands on the wheel, eyes on the road, ready to brake or steer immediately.
• Set conservative following distances and adjust for weather, visibility, and traffic conditions.
• Manually reduce speed for work zones, variable limits, and school zones.
• Keep sensors clean and unobstructed; heed alerts and disable ACC if sensors are impaired.
• Regularly review your owner’s manual for feature limits, updates, and towing or load restrictions.

Used correctly, ACC can reduce driver workload on suitable highways, but it is a supplement—not a substitute—for attentive driving.

Summary

You are not allowed to use adaptive cruise control as if it were self-driving, nor to abdicate attention, hands-on control, or legal responsibilities such as obeying speed limits and maintaining safe following distances. Do not use ACC in poor weather, complex urban areas, construction zones, or other unsuitable conditions, and never rely on it to detect stationary hazards. Keep sensors unobstructed, stay ready to act, and follow your vehicle’s specific guidance to ensure ACC remains a safe helper, not a hazard.

Can cops tell if you have cruise control on?

They have no way of knowing if your cruise control is on. But if they’re behind you, they can possibly tell that you had it on when they see the brake lights from you tapping the brakes to turn off the cruise control locked-in speed.

What are you not allowed to do when using adaptive cruise control?

WARNING: Adaptive cruise control is not a crash warning or avoidance system. WARNING: Do not use adaptive cruise control with a snow plow blade installed. The system adjusts your vehicle speed to maintain the set gap between you and the vehicle in front of you in the same lane.

What are common ACC problems?

Problems with ACC sensors are a common complaint. For example: Sensor Failures in Poor Weather: Rain, snow, or fog can block sensors, causing the ACC to stop functioning or to miscalculate distances. This can create a dangerous situation where the car fails to brake properly in response to slower traffic ahead.

What are the limitations of adaptive cruise control?

Adaptive cruise control (ACC) limitations include its failure to detect certain vehicles, such as motorcycles or pedestrians, poor performance in adverse weather like heavy rain or snow, and potential issues on winding or hilly roads. ACC is not fully autonomous and requires the driver’s active attention and responsibility, as it can have delayed braking, may not function in tunnels, and can lead to driver distraction or overconfidence, potentially increasing speed. 
Environmental & Road Conditions

• Adverse Weather: Heavy rain, snow, fog, or even water and slush on the road can block sensors and cause the system to malfunction, leading to inaccurate distance calculations or failure to brake. 
• Road Characteristics: ACC is primarily designed for highways and straight roads. It may struggle with: 
  • Winding roads: The system’s sensors and radar may not accurately track vehicles on curves. 
  • Hilly terrain: Slopes can impact the system’s ability to maintain speed and distance effectively. 
  • Tunnels: Environmental factors like those in tunnels can confuse the system. 
• On/Off Ramps: These demanding situations are not suitable for ACC use. 

Vehicle & Obstacle Detection Issues

• Limited Detection: ACC systems generally cannot detect pedestrians, cyclists, motorcycles, or low-lying trailers. 
• Stationary/Oncoming Vehicles: The system may not brake for stationary vehicles or objects, nor for oncoming vehicles. 
• Sudden Cut-Ins: A vehicle suddenly entering your lane may not be detected in time by the ACC system. 

Driver & System Engagement

• Driver Responsibility: ACC is a driver-assistance system, not a fully autonomous one; the driver must remain attentive and ready to intervene at any moment. 
• Distraction Risk: Overconfidence in the system can lead to distracted driving and reduced driver engagement. 
• Delayed Braking: The system can have delayed braking, especially when a vehicle rapidly approaches. 
• No Automatic Lane Changes: ACC does not change lanes automatically. 
• Phantom Braking: In some cases, phantom braking or unexpected acceleration can occur, particularly on winding or busy roads. 
• System Malfunctions & Recalls: Sensors can malfunction, and some ACC systems have been subject to recalls for safety concerns, according to William Mattar, P.C..