General Motors said it’s expanding its hands-free-driving Super Cruise Network of roads to 750,000 miles to make it North America’s largest such road system.

The Detroit-based automaker started the advanced driver assistance systems, or ADAS, network in the U.S. and Canada in 2017, calling it the first such network. It recently expanded it to 400,000 miles covering major federal and state highways. The newly announced expansion will take in minor highways connecting smaller cities but won't be fully in place until late next year.

GM’s ADAS is enabled by OnStar. It includes trailering capability, a feature the company says is exclusive to its vehicles.

It’s gradually making over-the-air updates to expand the network, though the Cadillac CT6 and Xt6 and the Chevrolet Bolt EV are ADAS-equipped vehicles that won’t get to access the expansion.