"Leave the driving to us." That's been Greyhound bus line's on-again-off-again tagline since 1956, only now it could aptly be applied to an infinitely more upscale mode of transportation: the Cadillac CT6. GM's much ballyhooed "Super Cruise" will go on sale in the fall of 2017 as a stand-alone option (as yet unpriced) on CT6 models with the premium luxury trim package and as standard equipment on top Platinum models (the price of which went up $500 for 2018, if that's any indication).

What is it? The rebirth of full-on Autopilot, which Tesla Model S and X owners enjoyed for a little while before a back-seat "driver" died in a crash despite receiving seven warnings from the car to resume control and the lawyers shut down that party. That system was never intended to, you know, actually be an "auto pilot," and this one's automatic piloting is considerably more restrictive than Tesla's cowboy over-the-air upgraded system. It's also fully vetted by what surely by now must be the jitteriest and most conservative lawyers in all of autodom.

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See all 23 photos

Highways only. The system only becomes available once you've entered a meticulously lidar-mapped, divided, limited-access highway in the U.S. or Canada—or a limited-access stretch of a highway that switches between on-ramps and crossings (like California Highway 101). When the steering wheel icon appears at the upper right of the central speedometer gauge, press the Super Cruise button, and when the car has locked on to the center of the lane, the light bar on the top of the steering wheel turns green.

Pay attention. Infrared emitters on the top quadrant of the steering wheel illuminate the driver's head and face, and a steering column-mounted camera with infrared capability (for night detection) constantly monitors head position and eye focal point. Look away for 15 seconds or less, and the system demands you return your gaze to the road by first flashing the green light, then flashing red, sounding a tone, vibrating the seat, and ultimately issuing a voice warning. If none of that succeeds in returning the driver to the task of controlling the vehicle, it will slow to a stop in the lane of travel, put the hazard flashers on, and summon help via OnStar. If you get to those last stages and resume control, Super Cruise locks you out until the next time you stop and restart the car. A nice touch: capacitive sensors detect the driver's hand(s) on the wheel, eliminating the need to wiggle it to verify control as with some lane keep assist vehicles.

You change lanes. Any deviation from the absolute center of the marked lane is on you. Want to avoid a pothole? That's your job. Need to change lanes to pass a slowpoke? Check your blind spot (the car will monitor it, too), signal, and steer into the desired lane (overcoming some resistance torque initially). The light bar on the wheel turns blue while you're driving. Center the car in the new lane and wait for the steering wheel bar to return to green, signaling Super Cruise is back in charge.

Reasonable weather. Autonomy is all about sensor fusion and multiple redundancies. Here the system relies on forward- and side-looking cameras, long-range radar, high-precision GPS (courtesy of Trimble), and a GM-proprietary high-def map database generated in conjunction with and maintained by a tech startup GM Ventures invested in called Geodigital). If the camera or radar data becomes compromised by heavy rain or snow covering lane markings or obscuring the radar unit or if the GPS system somehow goes down, the system will call upon the driver to resume control. Until that happens, the system will continue steering (or come to a stop as noted above), relying on all sensors that still work. Tunnels deprive the system of GPS, but maps keep it working for up to 1 km (0.6 mile), after which the driver is asked to take over.

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See all 23 photos

Construction zones. The owners' manual warns that the system is not programmed to cope with construction zones, but in practice it handles such zones OK if lane markings are provided and travel remains on the main road surface. But for example it will not follow even a well-marked deviation that crosses the median to share the opposite direction's roadway.

A few more interesting features:

Curve Speed Control. When Super Cruising, if the radius of a curve on a mapped highway would result in dangerous, uncomfortable, or unnatural lateral g levels, the car will automatically slow for the turn (and the cruise-control icon at the upper left of the main speedometer display indicates this system is active).

Regular and Adaptive Cruise. Whenever you're not on a Super Cruise-qualifying highway, you now have the choice of adaptive or ordinary cruise control. (Press and hold the cancel switch to toggle between these modes.) This feature is spreading across the whole Cadillac lineup for 2018. Oh, and the time-out length after which the system won't automatically resume driving in a stopped traffic jam is stretched from a few seconds to more like half a minute when in Super Cruise mode.

Pingpong lane keeping. In you-drive mode the Super Cruise sensors are still informing all other safety systems, such as the pre-collision warning and braking, lane departure warning, and lane keep assist. The latter still lets you wander from lane marker to lane marker because centering in the lane could mislead drivers into thinking Super Cruise was engaged.

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Sampling the system in an early-build 2018 CT6 Platinum, it functioned in a decisive way that instantly inspired confidence. Upon entering the freeway it quickly acquired the center of the lane and stuck to it faithfully, slowing quite gently when encountering slower-moving traffic then resuming the set speed in a timely fashion following a lane change. The infrared emitters and camera were able to penetrate my mirrored Oakleys with ease, and I was never hectored to pay attention or resume looking at the road except when I truly looked well away for extended times. There were no false alarms, in other words. One Tesla feature Cadillac is missing is the display indicating the actual path of the upcoming roadway with icons indicating car or truck traffic in the nearby lanes. The only display option is the typical adaptive cruise one with straight lane markers and a Cadillac CT6 rear end displayed when a vehicle is sensed ahead.

Super Cruise will effectively be the first SAE Level 3 autonomous vehicle offering for highway speeds. (The Audi A8 Level 3 system will shut down above a traffic-jam speed of 37 mph.) Company reps assiduously avoid using that terminology, however, perhaps because competitors such as Ford and Volvo have made a big deal of their intentions to skip over Level 3 and go right to Level 4 "full autonomy," in which the vehicle is "designed to perform all safety-critical driving functions and monitor roadway conditions for an entire trip" (when traveling on mapped roadways—Level 5 is full humanlike go-anywhere autonomy).

I'll admit I was saddened when Tesla over-the-air "upgraded" Autopilot to require hands on the wheel every few minutes. I'm heartened to see Cadillac introducing a hands-free—and fully vetted—replacement for that pioneering system.

Read more about the Cadillac CT6: