General Motors' futuristic semi-autonomous driving technology now seems tinged with nostalgia.

The automaker's "Super Cruise" self-driving function was first announced back in September 2014, but the new model many expected to be launched with the feature - the 2016 Cadillac CT6 - showed up without it.

Now, GM plans to debut the feature next year, and a recently intercepted letter from the federal government shows what to expect from the system.

Super Cruise allows drivers to let the vehicle take over some piloting duties on the highway and in traffic, but it's not a fully autonomous system. It seems to be less capable than Tesla's old Autopilot, but that could be on purpose. (We all remember the trouble that company's self-driving system created.)

According to Reuters, a letter sent to GM from the National Highway Traffic Safety Administration describes how vehicles equipped with the technology will automatically pull themselves over and stop, hazard lights flashing, if drivers go too hands-off.

The shutdown mode becomes activated if a road becomes too twisty for the system to navigate, or if a driver fails to respond to repeated alerts. Still, the country's road safety regulator worried about the shutdown process. In its letter, NHTSA asked GM to "ensure that this fallback solution does not pose an unreasonable risk to safety."

It seems that the shutdown mode is a drowsy driver's best friend. A GM spokesperson told Reuters that Super Cruise includes facial recognition technology that issues alerts to prod a distracted or drowsy driver back to awareness. The alerts include a flashing gauge cluster light, seat vibrations, an audible warning, and eventually the voice of an OnStar representative.

If there's no response, it's assumed the driver is incapacitated and the system activates shutdown mode.

Barring another setback, expect to see Super Cruise offered on a Cadillac model sometime in 2017.