Two sunny days in late September, a state-of-the-art luxury sedan, and good company make for a potentially great road trip. But this one was special.

“Pretty remarkable that we’ve already driven about 500 miles without either of us touching the steering wheel; I’m impressed,” I noted to co-driver Sam Abuelsamid, as we headed southbound from Chicago, on Interstate 57 in Illinois.

Sam, a former electronic systems engineer-turned-journalist, analyst and Automotive Engineering columnist, concurred. “It appears this is the vehicle to have if you want to reduce the driving workload over long distances,” he offered.

We covered another 200 miles (321 km) of hands-free operation before re-taking the wheel of the 2018 Cadillac CT6 as we neared our Memphis destination. Of the 900 miles (1450 km) we’d traveled since leaving Cleveland the previous day, over 75% were handled by GM’s new Super Cruise technology. In terms of the SAE automated-driving levels, Super Cruise operates at Level 2, or ‘partial automation.’ This means the vehicle drove itself in certain situations under human supervision, and re-engaged us to pilot when appropriate.

GM’s flagship sedan is the first to feature Super Cruise, best described as an automated driver-assistance package. Demonstrated five years ago, the system was slated for 2016 launch. But GM wisely pushed the ‘pause’ button after the company’s tragic, multi-billion-dollar ignition switch recall and a traffic fatality involving Tesla’s erroneously named Autopilot. Various YouTube videos of ludicrous Tesla drivers climbing into their cars’ back seats during Autopilot operation also caused GM engineers and safety experts to move Super Cruise forward more cautiously.

By summer 2017 the system had been fully developed and validated and was readied for the CT6 application. To demonstrate its confidence in Super Cruise, GM invited media to drive a small fleet of CT6s from New York to Los Angeles, in three waves of roughly 1,000 miles each. Sam and I chose the second wave on the Cleveland-Chicago-Memphis leg. Most of our journey was on U.S. interstate highways and multi-lane divided state freeways because currently they are the only types of roads for which Super Cruise is operationally mapped.

Benchmark driver monitoring

GM engineers and human-machine interface designers created a system that is easy and intuitive to operate. Press a marked button on the left steering wheel spoke, center the vehicle in the lane, and an icon will appear in the cluster signaling that the system is ready for use. Press the button again and the icon turns green, as does a light bar inset into the upper radius of the steering wheel—Super Cruise is thus engaged and the CT6 steers itself along the highway at speeds up to an ‘official’ 80 mph (129 km/h), although a few journos said they saw 90 mph (145 km/h) while in Super Cruise mode.

With the driver’s hands off the wheel, the vehicle consistently follows lane markings and stays centered, even when the lines are faded and non-existent, such as on fresh asphalt. Sam and I each “drove” for intervals of an hour or more without touching the steering wheel. Passing other vehicles does require the driver to press the throttle pedal but Super Cruise then resumes operation when the pedal returns. Pressing the button after manual braking also re-engages the system.

Primary hardware includes three exterior cameras; one is forward-looking and mounted in the rearview mirror module. The other two are located on the exterior mirror housings. There are also five radar sensors, one a forward-looking long-range unit and the others short range/side-looking, mounted in the front and rear corners. After entering a tunnel, Super Cruise remains engaged for up to 0.6 mi (1 km) at which point dead reckoning takes over.

Another vital element is Super Cruise’s Driver Attention Monitor. Its performance is benchmark: Infrared emitters in the light bar within the steering wheel rim project thousands of invisible points of light onto the driver’s face, which are then captured by a small, almost unnoticed camera located on the steering column. The system monitors position and movement of the driver’s head, face and eyes—are you looking forward and attentive to the road ahead? Are your eyes closing due to sleepiness? Behind our dark sunglasses, Sam and I each tried to ‘trick’ the system by fluttering our eyelids and rolling our eyes but it was never fooled.

Super Cruise will require some CT6 owners to adapt. The time it permits the driver to scan the mirrors or select an HCAC setting is mere seconds, and is speed-dependent. It won’t let you ogle that Ferrari passing in the opposite lanes or check out that cool old barn along the roadside before it starts to escalate driver intervention, as explained below.

Sam and I agreed that the overall quality of GM’s sensor fusion and calibrations, based on our perception of how smoothly Super Cruise keeps lane, handles curves, and brakes itself is superior to any SAE Level 1 vehicle we’ve tested to date.

Maximum sensing-distance capability is 2500 m (1.5 mi), noted Robb Bolio, the Vehicle Performance Manager who accompanied our media wave. He said the sensor array and the system controller are all sourced from GM’s regular ADAS component vendors. System software was developed in house and Trimble supplied Super Cruise’s GPS that’s accurate to 2 m (6.5 ft).

There is no lidar; GM enlisted Atlanta-based Ushr (formerly part of GeoDigital) to digitally map over 160,000 miles (257,500 km) of divided highways in the U.S. and Canada. The resulting precise, high-definition 3D maps are the heart of the Super Cruise software.

“It ‘geofences’ the highway,” Bolio noted. “No back-road, town or urban capability at this point.” The map data “provide accurate details of road curvature, trajectory and annotations,” he said, and will be over-the-air updated for customers at Cadillac dealers initially. During the 900-mi trek, our car remained consistently centered and faithful in most cases where lanes merge or end; a few times it did attempt to exit a couple off-ramps for a split second before snapping back into the intended lane.

Here, you take the wheel

If you’ve been distracted for five seconds, the driver monitor begins a steady and rapid warning escalation to regain your attention. The green Super Cruise icon on the cluster and the light bar on the wheel begin flashing and audible chimes in. There’s also a driver-select haptic seat “buzz” pioneered by Cadillac that’s quite effective in jogging your attention. Less than five seconds later, if the driver hasn’t responded the flashing lights turn red and the audible and haptics heighten.

Another five seconds without driver response (the car must “feel” driver contact via capacitive sensors in the steering wheel rim) and Super Cruise begins to slow the car’s speed toward a stop—which it will also do, smack dab in the lane. Bolio explained that GM research concluded that stopping in the road is safer than on the shoulder, which often doesn’t exist. As the car decelerates, it also shuts off the Super Cruise function until the next time the driver turns off and on the ignition. During a full vehicle stop the system calls OnStar for help and alerts first responders if emergency medical care is required.

By design, GM’s Super Cruise as employed in the 2018 CT6 has what some may consider to be limitations. Others, however, including me will applaud them as well-reasoned conservative steps toward the ‘higher’ levels of SAE autonomy. That the five-second limit requires driver attention and minimal head and eye movement proved not to be relaxing on 900-mile journey. In fact, I found my typical sense of highway-driving alertness to be heightened considerably. The driver must be prepared to take back control at any time.

Super Cruise currently will not change lanes—that’s a manual task left to the human. It also doesn’t read speed-limit signs like the Mercedes system in the E-Class, although it’s capable of doing so. Nor will it transit through a cordon of Jersey barriers in construction zones. In at least one hands-free situation with me behind the wheel, our CT6 handed control back to me abruptly a few feet after entering a single-lane-with-concrete-barriers construction zone.

And we media types on the second-wave drive complained that the system stubbornly would not engage as we departed Cleveland, when the bright morning sun was behind us. Bolio was aware of this issue, explaining that infrared wavelengths contained in the sunlight entering the car at specific angles can foil the emitters in the driver-monitoring system. The monitoring camera then cannot ‘see’ the driver’s face and so will not engage Super Cruise until the sun rays entering the car diminish.

As a system, Super Cruise by my estimate may cost GM $400, a figure Cadillac will easily recoup in its $5000 option pricing. The system is standard on Premium-trim CT6 models. Dealer sales staff are advised to give test drives only when the sun is high in the sky. Competitors, however, are already lined up at Cadillac dealers to order Super Cruise-equipped cars for their teardown and analysis.