Cruise control may, indeed, help you squeeze out a few more miles per gallon when you’re driving on open and level stretches of highway and when the traffic is light and moving smoothly.

A cruise-control system keeps your car at a constant speed by regulating the flow of fuel to the engine. This saves gas primarily by preventing needless speed changes. Some drivers find it difficult to keep a steady foot on the accelerator, and the repeated surging that results wastes gas. Cruise control also forces drivers to focus on a broader view of the highway, which reduces the possibility that they’ll overreact (with constant quick decelerations, say) to inconsequential changes in traffic or road conditions.

Finally, given the fact that a driver’s average speed tends to increase the longer he or she is on the road (a phenomenon called "speed creep"), cruise control helps the vehicle maintain a slower, more fuel-efficient pace.

Real-world test results demonstrate that cruise control may improve fuel efficiency by 4 to 14 percent.