What is adaptive cruise control (ACC)?

Buying a new car doesn’t have to be a difficult thing – after all, that’s why we started carwow.

One of the hardest things you’ll encounter when buying a car is deciphering the dozens of TLAs (that’s three-letter acronyms!) car makers use to describe technology.

We’re here with a series of guides to help explain some of the more modern technologies that you might not have seen on a car.

This week, we’re looking at adaptive cruise control (ACC), otherwise known as DISTRONIC Plus (Mercedes), Active Cruise Control (BMW, Citroen and more), or Porsche Active Safe.

What is it?

People have always strived to make make the chore of driving that little bit easier to stomach. The invention of cruise control is a prime example – by maintaining a constant speed without human input, your common or garden cruise control helps reduce the hassle of long motorway slogs, and even removes the anxiety of accidentally creeping over the speed limit through speed camera zones.

How normal cruise control works

Variants of cruise control have been in use even before the creation of the car: the inventor and mechanical engineer James Watt developed a version as far back as the 17th century, which allowed steam engines to maintain a constant speed up and down inclines. Cruise control as we know it today was invented in the late 1940s, when the idea of using an electrically-controlled device that works out road speeds and adjusts the throttle accordingly was born.

A regular cruise control system simply does what is told to do. It makes for a rubbish co-driver, in other words. If a lorry pulls out ahead of you on the motorway, you will need to take over and regain control until it moves out of the way. In recent years, cruise control has moved on, becoming ‘adaptive’, aiming to further ease the pain of the most tedious aspects of driving.

How does adaptive cruise control work?

ACC combats the shortcomings of the basic system by using several radars – and sometimes cameras too – to calculate the proximity and relative speed of other vehicles, up to several hundred meters ahead (if you look closely, you can tell when cars are equipped with the feature: you’ll normally find a little ball-shaped device hidden behind the front grille.)

With these two variables, ACC can decide whether it should maintain a constant velocity, or if it needs to slow the car down. Some can even bring the car to a complete halt if needed, which means that throttle and brake applications are no longer required in slow-moving traffic. If an emergency stop is predicted, then the driver is warned via an audible beep and warning sign, as most ACC systems are not designed to perform such a manoeuvre themselves.

Most systems will automatically illuminate the brake lights if they have to slow the car down quickly, so you don’t need to worry about people running into the back of you because of a cruise-control-initiated stop.

Some ACC systems make the use of GPS (global positioning system) too, which can benefit ACC in two ways. First, it can monitor the topography of a road, allowing it to adapt to road conditions to improve fuel efficiency. Secondly, it can combine information with a forward-facing camera in order to decide whether the car in front is slowing down for traffic, or simply because a slip road is ahead and they have indicated to take the next exit.

Don’t confuse ACC with automatic emergency breaking systems that will slam the brakes on if they detect anything in the road ahead (such as the wayward elk below) – ACC is unlikely to help in these situations.

Who uses it?

ACC is becoming quite a common feature in new cars. Mercedes, most Volkswagen Group cars, Ford, and BMW, to name a few, all use Adaptive Cruise. Many higher end cars feature the tech as standard, but models such as the Mercedes A Class feature it as a pricey option (£880).

Any drawbacks?

It’s all very well that ACC can drive at a constant speed itself, but if the person ahead drives erratically then the car will follow a similar pattern too. This will be mitigated by maintaining a greater distance from a car such as this, but it can still be mildly irritating.

Anything else I need to consider?

The ACC technology varies from one manufacturer to another. BMW and Audi systems, for example, feature Stop and Go, allowing it to stop and start in heavy traffic. Ford’s design on the other hand, does not work under 20mph, so make sure you know the limitations of the tech before you bump your shiny new Focus into the car ahead assuming your car would stop for you!

Other systems – such as the one offered by Porsche – are only available with models fitted with automatic transmissions, which means that you may end up spending quite a significant amount of money for the privilege.

Is it worth it?

We at carwow are all for it. Nobody enjoys driving on a motorway very much, and getting stuck in a traffic jam is even more universally disliked. Anything that can take the bother out of such mundane aspects of driving can only be welcomed. It is genuinely a step towards autonomous driving, too, which has to be considered an exciting step.

Just be warned – the first time you feel ACC working is usually quite disconcerting! Once you get used to it you’ll wonder how you did without it, especially if you spend a lot of time on motorways.

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