Ready for a self-driving car? Check your driveway.

Full self-driving vehicles take to the road in some states, but plenty of older cars already have autonomous features. 

Last month, Nevada became the first state to license driverless cars. It issued special plates for eight vehicles to navigate public roads using only sensors, global positioning information, and artificial intelligence.

The law requires two people to be in the car while it's moving. One monitors the computer system as it scans for bends in the road, nearby cars, and pedestrians. The other sits behind the wheel, ready to take over in case anything goes wrong.

Google, who owns this initial fleet of self-driving vehicles, says it's logged more than 200,000 miles without incident. The technology will require much more testing before fully autonomous cars roll themselves into dealers' lots. Still, pieces of this research exist in cars today.

"In the near term, we're likely to see increased driver assistance," says Bryant Walker Smith, a fellow at the Center for Automotive Research at Stanford University in California. Few people are ready to put a car on autopilot, but, through baby-step innovations, "technology will really become something of a copilot."

Commercially available vehicles can already parallel park on their own. Drivers only need to line up the vehicle and put the car in reverse. A computer takes over, turns into the spot, and beeps when it's time to apply the brakes.

This is just the beginning.

BMW is testing a system that can temporarily take the wheel in an emergency. Should a driver become incapacitated, "a car driving at Autobahn speeds, in the fast lane, will drive in a safe way to the shoulder, come to a complete stop, and send an SOS," says Panos Prevedouros, professor of transportation engineering at the University of Hawaii at Manoa.

The 2013 Subaru Outback comes with several autonomous features that Mr. Prevedouros says have been common in Europe for years and recently have trickled into vehicles sold in the United States. Its "adaptive cruise control" matches speed with the car in front of it, keeping a safe distance even in stop-and-go traffic. Additional sensors watch lane markers and will chime if the driver drifts across the road.

These features and Google's cars in Nevada aim to make driving safer. Vehicle crashes are the leading cause of death among Americans ages 5 to 34, according to a federal study from 2010.

"Google is the most public, but automakers all have autonomous test vehicles," says Mr. Smith. "When the technology is there, it's difficult to imagine that it wouldn't be on the road."

For more on how technology intersects daily life, follow Chris on Twitter @venturenaut.