A potential fuel (and licence) saver on the highway
Potential Fuel Saving: Up to eight per cent, highway
Worthwhile … if you’re a leadfoot, or erratic
On 110km/h freeways it’s actually possible to beat the cruise control’s economy if you use the throttle extremely sensitively. (We managed a two per cent positive margin without dropping back from the prevailing traffic flow, but you must drive as though the accelerator has a big spike pressing into the sole of your foot.)
If, however, you drive assertively, without regard for consumption but reasonably within the speed limit, you will never look like getting close to the economy afforded by cruise control set to the legal limit.
Cruise is also a potential licence-saver on long trips, at least sometimes. But on this issue, it's worth noting not many cruise control systems adapt to steep downhill sections. These tend to pull the car's speed up into 'but officer' territory. With the cruise set to 110km/h the Calais ran up to an indicated 124km/h on one particularly steep descent on the freeway. Use the cruise to protect your licence if you find your speed creeping up, but you still need to watch your speed on the downhill runs.
If you put the fuel saving in perspective, the average Australian motorist might save, on average, about $1.40 a week for all the highway running if they use the cruise control - about $70 annually. But if using it stops you getting booked for speeding just once, you just tripled your saving without compromising your licence.