Cruise control is not an auto pilot system and does not relieve drivers from monitoring traveling speed and deciding when to adjust it. The best conditions for using cruise control are straight highways with clear dry road conditions. Conditions in which many speed adjustments are required are not suitable including winding roads, heavy traffic, and city and suburban streets. Most cruise control systems will not operate below speed limits close to urban minimums like school zone limits (30 km/hr), for example.

 

A cruise control system controls the speed of the car by adjusting the throttle position and actuating the throttle valve by a cable connected to an actuator instead of by the cable connected to the accelerator pedal. In effect, fingertip control replaces foot-on-the-accelerator-pedal control. While each vehicle model has its own refinements, most have a button that turns the system on and off. Once the desired speed is attained, pressing the set button, which is usually located close at hand somewhere on the steering wheel, tells the vehicle to maintain the current speed. Tapping this same button makes the vehicle accelerate by a pre-set rate. Tapping another “Decel” or “Coast” button will make the vehicle decelerate by a pre-set rate. Hitting the brake pedal disengages the control. Hitting the set or resume button restores the most recent speed setting.

 

A good cruise control system accelerates aggressively to the desired speed without overshooting it, and then maintains that speed with little deviation no matter how much weight is in the car, or how steep the hill ascended.

 

Cruise control is not recommended on icy or wet slippery roads.  The system reacts to loss of traction by accelerating, and having to hit the brake to disengage it only compounds the problem.

 

Studies on the effectiveness of cruise control systems in reducing the number and severity of speed related crashes are few as are statistics on how much they are actually used. Constant, even vehicle distribution and driving gaps over long distances may indicate usage. Their effect on fuel efficiency is also unclear. Less abrupt change in speed is generally more conserving, but, on the other hand, cruise control tends to over throttle on the upgrades and retard on the downgrades, thereby wasting the energy storage capabilities available from the inertia of the vehicle. But, improvements are on the way.

 

The next refinement, adaptive cruise control (ACC) uses radar to measure the distance to the vehicle ahead. In addition to maintaining a set speed ACC will automatically regulate both the vehicle speed and its distance to the vehicle ahead traveling in the same lane. This new technology may prove to be the biggest safety improvement in decades.