Sadly there's no such thing on the A6, and it caught me out recently at the Dartford Crossing when, for the first time in living memory, I had to queue with the trucks and pay with a note rather than slip through the autotolls unhindered.
It's these small details that make the difference in everyday motoring, and which can have quite an impact on journey times. I reckon it took me all of four minutes to get through the toll booth which, if you are averaging 60mph, equates to four miles on the road – four miles nearer my destination.
The same theory applies to the time spent filling up: it stands to reason that the better your fuel economy, the less time you'll spend on the forecourt and the shorter will be your journey times. A real case of tortoise meets hare.
So it's good to report that, gradually, the A6's fuel consumption is improving. Last time, I reported an average of a disappointing 33.8mpg – a far cry from the official combined figure of 39.8mpg. Now, however, with more than 3,000 miles recorded and with the engine nicely loosened up, I've seen a marked improvement, up to 35.6mpg and often significantly more on a run. It does your conscience good, especially when compared with equivalent petrol cars: the A6 2.4 SE auto returns 28.8mpg combined, for example, while a Saab 9-5 2.0t SE auto is good for just 26.6mpg.
The Multitronic transmission has become more responsive, too, though there's still an annoying hesitation from a standing start. The quicker, smoother downshifts mean there's now no need to select manual mode if a quick burst of speed is needed for overtaking.
I'm relishing the A6's serene cruising ability and smooth ride which makes light work of a long motorway haul. And although the boot doesn't put the Avant among the biggest load luggers on the road, it's proved big enough for all the family's paraphernalia on a weekend away.
I'm less confident about the champagne-coloured interior's ability to stay pristine, however. It looks classy and feels great, especially with the walnut wood veneer inserts on our car, but I wonder how it will resist scuffs and stains over the coming winter.
Other criticisms? Not many, though I'd like a bit more power – answered by the latest spec 2.5 TDI which now develops 163bhp – and engine refinement could be better. Compare the A6 at tickover with, say, a BMW 530d or Mercedes-Benz E270 CDI and there's no contest on engine noise, though thankfully little seems to get transferred to the cabin.
Tax payable (40%): £203 per month