They're a tiny part of the car market, but limousines are crucial flagbearers for luxury brands, typically laying the foundations for the rest of the range – often introducing new technologies.
For Audi, that limousine is the A8, a car that's never sold well in Australia; the rival Mercedes-Benz S-Class and BMW 7-Series have comprehensively outsold it for decades.
But Audi is hoping for bigger things with its latest A8, codenamed D5.
The new A8 has size on its side. The D5 is 37mm than the D4 it replaces and its roof is 13mm higher.
Splash out another $15K and you get the long wheelbase, with an extra 130mm in the back.
That's important for a limo; back seat space is, after all, a big part of the comfort equation.
As with the original A8 of 1994 the latest one uses aluminium extensively in its body.
However, Audi has also introduced magnesium, high tensile steel and even carbon fibre to stiffen the structure and reduce weight.
That drive to push the boundaries is something on display elsewhere, particularly when it comes to electronics.
The A8 includes many driver assist systems similar to those used in rivals, including steering assistance and radar cruise control that allows semi-autonomous driving for short distances.
However, the A8 is the first car to feature a laser scanner, or lidar, which teams with radars, sonar and cameras to form a more accurate digital picture of the surrounding landscape and road users.
It also has a powerful central computer analysing data from the various sensors to ensure it reacts appropriately.
Don't let go
The A8 may have more hardware, but it doesn't do anything more than rivals – blame that on regulators.
The A8 has the potential to take full control on well-marked roads and in traffic below 60km/h.
However, such level three autonomy is currently not offered for Australia.
Our test gave an inkling to the hesitation of authorities.
In 1000km of driving – much of it on country roads – the car twice braked unnecessarily.
And, like all cars with semi-autonomous freeway driving – BMW, Mercedes-Benz, Volvo and Tesla are top of the list – there's no relying on it away from well presented freeways. Humans are still much better than the technology on B-grade country roads.
A remote parking feature has also temporarily been disabled, although Audi is hoping to gain approval to connect it soon.
For drivers, then, it's back to basics in the A8, a car priced from $192,000 for the 50 TDI diesel or $195,000 for the 55 TFSI petrol.
Occasionally a sharp edge will catch it out, but comfort levels are excellent.
But there's nothing especially exciting about its manners, the steering lacking some feedback, for example.
And the 3.0-litre V6 turbo diesel in the 55 TFSI model is nothing special. There's 250kW to play with, enough to help it on its way to 100km/h in 5.6 seconds.
It works nicely with the eight-speed automatic, too.
But there's no zing or spark to the way it works, the muted exhaust sound in keeping with the luxury flavour.
Instead, the engine's party trick comes with its partial hybrid system, which can capture up to 12kW of power when decelerating or coasting.
Flick the switch
Unlike traditional hybrids, though, the electric motor never drives the car.
Instead, the engine recuperated during deceleration is used to power ancillary electrical items through a 48-Volt network (others have 12V systems) as well as restarting the engine once it's temporarily switched off.
While it also shuts down when stationary, the A8's engine can switch off when coasting, seamlessly refiring when you accelerate.
Inside, the A8 has undergone an overhaul, particularly with its infotainment and operation systems.
A 10.1-inch upper screen manages audio and navigation systems, with familiar swipe functions. There's also haptic feedback, the screen kicking back subtly to confirm it has received the instruction.
Those in the rear aren't forgotten with touchscreens, either. Fold down the sizeable centre arm rest and there's a removable 5.7-inch screen that allows those out back to choose the audio, set ventilation controls and even control the overhead matrix LED reading lights, which can tailor the spread and direction of the beam.
The general presentation of the interior has also evolved enormously, taking on a more organic look dominated by horizontal lines.
Natural woods and leather are mixed with metal touches and upmarket plastics for a quality look and feel.
The A8 also showcases the best of Audi's more familiar modern technology.
Key to that is matrix LED headlights, now with 32 individual LEDs on each side.
They fire a long way down the road but also do a superb job of allowing high beam use around other road users, selectively blanking out other cars while illuminating plenty elsewhere.
Their standard fitment is indicative of a step up in standard equipment for the A8, which incorporates a head-up display, sunroof, four USB chargers and a 17-speaker Bang & Olufsen sound system.
It's a heck of a lot of car packing in plenty of technology – arguably making it the smartest car on the road.