Cadillac's flagship CT6 might not have the best interior in its class. It might not have the sharpest, track-honed handling. It doesn't have a butter-smooth V12 engine. It definitely doesn't have the best infotainment system. And yet, it is carrying the most exciting technology being offered in any production vehicle on sale in 2018.

Called Super Cruise, Cadillac's new tech represents the best semi-autonomous system on the market. In fact, Super Cruise is so good, I think General Motors needs to do everything it can to add it to the company's entire model range, post-haste.

You sure sound excited about this thing

Regular readers will know this isn't the first time I've written about Super Cruise. In fact, at last year's New York auto show, we awarded it an Ars Best distinction in the "Automotive Technology" field—a bold move for new technology that we had yet to actually test.

But with almost 900 miles of Super Cruising under my belt now, I am glad to report that boldness paid off. This system really is that good. As long as its operational conditions are satisfied, Super Cruise will enable the CT6 to accelerate, brake, and steer without any need for you to touch the pedals or steering wheel. This can happen for hours at a time.

At its essence, Super Cruise is another one of those systems that combines adaptive cruise control and lane keeping. Forward-looking sensors measure the speed and range of any cars ahead of you to maintain a constant distance and also read the lane markers on either side to keep you centered within it. So far, so much the same as any number of systems from any number of OEMs. But Super Cruise adds a couple of other features that are missing in every other implementation—even in Tesla's much-loved, somewhat-infamous Autopilot. What's more, Super Cruise's unique features will be critical for true self-driving cars in the future.

First up is the driver monitoring system (Cadillac calls it a Driver Attention System). This isn't entirely unheard of; various car makers have been putting crude monitoring into vehicles to warn drivers when they might be getting too drowsy. The CT6's DMS lives just on top of the steering wheel column, pointed at your face. Don't worry! It's not doing anything creepy like detecting your emotional state. (Do worry! Those kinds of systems are only a few years from showing up in our cars.)

Rather, the CT6 uses gaze tracking to know what you're looking at. Here we encounter the first of the required conditions for Super Cruise to operate: you must be paying attention to the road ahead. Stop doing that for too long and a series of ever-more attention-grabbing alerts will follow. Keep ignoring those, and the system will disengage. Eventually, it will slow to a stop if there continues to be no driver input.

Ambient light isn't an issue, because the steering wheel rim contains a number of infrared LEDs to illuminate you even in the dead of night, and DMS had no problems "seeing" my eyes even when I was wearing polarized sunglasses. If the DMS can't see you because its line of sight is blocked by an object, it reacts the same way as it would if it could see you but you weren't paying attention.

The second big difference between Super Cruise and everyone else is that it is geofenced. Regular old adaptive cruise control can be engaged anywhere. And lane keeping assists that autosteer for you only care that their optical sensors can read the lane markings. But Super Cruise is a bit pickier. It will only activate if you're driving on a divided, limited access highway. More than that, it also has to be a highway that GM has lidar-scanned and added to its HD map, something the company has done for more than 160,000 miles (257,500km) of highways in the US and Canada thus far.

If both those conditions are satisfied—driver paying attention; car driving on a mapped, limited-access highway—you're good to go.

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Engage!

Before you can engage Super Cruise, you need to be already using cruise control (on non-mapped roads this works just the same as every other adaptive cruise system). Once you see a white Super Cruise icon on the instrument display, you can turn it on via a dedicated button on the multifunction steering wheel. At this point, the magic happens. The icon on the dash turns green, but more importantly so does a big, bright LED strip set into the top portion of your steering wheel. And now, you can go hands- and feet-free. As long as that light strip is green, Super Cruise is happy.

Take your eyes off the road for too long—about five seconds by my reckoning—and the warnings begin. The first of these starts the steering wheel light bar flashing. It remains green, but it wants your attention back on the road ahead.

Keep ignoring it and the alerts become more urgent. The light bar now flashes bright red, and there will either be audio warnings or the seat will start to vibrate angrily. (The choice of audio or haptic alerts is user-configurable.) Should you continue to ignore all of those warnings and keep your focus somewhere other than the straight ahead, Super Cruise disengages.

But I thought Autopilot was the best system in the world? Up until this point, you probably thought Tesla's Autopilot was the closest thing to a self-driving car any of us could buy. Certainly, when Lee Hutchinson did his 400-mile Model S road trip in 2016, that was probably true. But it's not true today. For one thing, the Autopilot Lee used back then is different from the system currently being installed in Teslas. After falling out with supplier Mobileye, the electric car maker decided to go it alone, and the so-called Hardware 2 system, designed completely in-house, has yet to fully match the original system's functionality. For another, even though Autopilot will let you go hands-free for long stretches, its driver monitoring system is just a torque sensor on the steering wheel. YouTube is full of videos showing users defeating this feature with water bottles and citrus fruit, and this poor operational design was fingered by the National Transportation Safety Board as a factor in the fatal crash of Joshua Brown's Model S in Florida in 2016. For a more in-depth comparison of Super Cruise and Autopilot, I highly recommend this feature by Alex Roy over at The Drive.

The system will also use the red light bar and vibrations to alert you about an imminent disengagement, handing back control to the human. Unlike the "Level 3" driverless systems we've seen, Super Cruise doesn't give you 30 seconds to take back control, but then again it has been designed not to have to solve that problem. As long as it's active, Super Cruise knows you're paying attention to the road, so there shouldn't be any surprises.

When running, Super Cruise is an extremely good driver. It does not veer from one side of the lane to the other, and if the speed is set too high for an upcoming curve it will slow you down before you reach it. If you need to change lanes or adjust your trajectory in any other way via the steering wheel, the green LED will change to blue, and you have full control of the steering.

To return back to Super Cruising, simply let go of the wheel, and the LED turns green again. Like all cruise controls, dumb or otherwise, using the brake pedal will disengage it all. But if you need (or want) an extra burst of speed, using the accelerator will not interrupt it, it will merely make you go faster. Take note, this only works up to 90mph: exceeding such speeds will also cause the system to disengage.

Critics repeatedly point to "mode confusion" as a reason we shouldn't pursue anything other than completely self-driving vehicles, pointing out that crashes happen when a driver thinks the car is in control, but the car expects the driver to be actively driving. And they're not wrong. I experienced this while testing a Volvo XC60 recently on at least two occasions when I thought its Pilot Assist system was running when in fact it was not. I don't think that would ever be a problem with Super Cruise, which is even less ambiguous about which mode you're in than Nissan's ProPilot Assist.

Again, this is a limited system that doesn't work everywhere. During my testing (mainly on the highways between DC and Charlotte, North Carolina), I found it would disengage at highway junctions and also (but not always) when road construction meant the highway was narrowed and off its usual course. If I had one complaint, it would be that Super Cruise places the car slightly closer to the right-hand lane boundary than I'd prefer. But beyond that tiny quibble, I was deeply impressed with its ability to get me home from Charlotte safely after a long day of meetings and demos (with NASCAR, something you can read about in the next few weeks).