Our Kia long-termer is among a growing army of cars fitted with stop-start technology, which is intended to reduce fuel use and emissions.
The idea is simple. When the car comes to a halt and it is in neutral, the engine turns off. When you depress the clutch, it comes back to life before you have time to get into gear again.
This system has worked faultlessly on our Kia Optima for more than 10,000 miles, although I have been surprised that it is only active for around 90 seconds – presumably to stop the battery from becoming drained.
As a result, I began to question its value in saving money, after all how much fuel does a car use in 90 seconds?
A few minutes tapping data into a spreadsheet has provided the answer and it’s more encouraging than I thought, depending on your driving profile.
To answer the first question, the Optima sips roughly 0.3 gallons of diesel per hour when idling, or 1.37 litres. That equates to 0.023 litres a minute.
From that point onwards, how much you save depends on your driving profile. I estimate that I have the equivalent of five 90-second stops a day, which adds up to 0.17 litres or around 24p.
It seems barely worth the effort, but over a year, that becomes £90 and over a three-year cycle £240, although that does assume you tick off these savings for every one of the calendar’s 365 days.
The real savings come when you start commuting and using the system to its fullest extent.
Those unlucky enough to endure the leg-numbing, clutch burning hell of a London or M25 commute, complete with stuttering progress on local roads, could realistically expect the equivalent of 40 full stop-start ‘episodes every day, equivalent to half an hour standing still each way.
In this case, the figures suddenly become more interesting, with potential fuel savings of nearly £2 a day, £725 a year and £2,175 over a three-year cycle.
Even if you halve these figures to account for holidays and good traffic days, the savings remain respectable enough to justify stop-start being standard fit on most fleet vehicles.