It sounds like something out of science fiction, but the self-driving car is a reality that many people are already seeing on the road.

One of the major developers of self-driving cars is Google with their Self-Driving Car Project. Google is actively testing the cars on the roads of three U.S. cities right now. They aren’t the only ones, but they’ve been great about putting materials online and sharing how the cars are being developed for everyone to see.

Below are five things you should know about self-driving cars.

1. This Isn’t Star Trek – It’s Happening Now

This is happening. Google’s cars have already test driven over a million miles on U.S. roads. You may have seen them yourself.

And they aren’t the only ones doing this. BMW is pushing hard for their own version of a self-driving car, as is Nissan. Tesla has already activated some self-driving features in their cars and continues to develop new features for existing cars and more autonomous cars for the future.

2. Some Form of This Is in Cars Already

Google’s project is 100 percent self-driving cars. But, as alluded to above, there’s a range of what the industry refers to as self-automation. Tesla has some of this automation built in already and it’s coming to more and more cars.

Fully self-driving cars are expected to be on the roads in 2019. At that point, many expect that there will be 10 million cars on the road that contain some form of self-automation, making an incredible number of cars on the road capable of making decisions on their own.

3. The Cars Increase Safety

One of the great benefits of self-driving cars – besides freeing commuters to do something besides navigate that gridlock – is increased safety. A cartoonist who draws at The Oatmeal got a ride in one of Google’s self-driving cars and described it as a “timid” driver that always makes the safe decisions.

The cars have been tested to be safe, and it’s part of the design process. The developers want these to provide a safer form of transportation.

The Google cars had driven 1.4 million miles without a single accident until earlier this year when one of their cars had a collision with a school bus while the self-driving car was going two miles per hour.

Barrons reports that the Internet giant is so confident about the safety of their cars that Google is willing “to accept liability if its self-driving cars cause an accident,” in an effort to help any insurance problems they might encounter.

4. There Are Technological Obstacles

There are many hurdles to clear before fully autonomous self-driving cars are taking over the streets. Some of those issues are technological. The cars still have some difficulty with extreme weather.

The cars can have a tough time seeing through fog, heavy rain, or heavy snow.

There are also practical problems like understanding humans, who can be unpredictable. The technology needs to be able to read the impulses of human pedestrians or other humans driving cars in situations like a four-way stop. The cars are succeeding, but there are challenges to be conquered in that regard.

5. And Then There Are Even More Obstacles

There are many regulatory obstacles. Does the owner of a car need some kind of pilot license to have a self-driving car? If cars drive themselves, how old do you have to be to be in a car by yourself? How autonomous can a car be? Does there need to be someone in the driver’s seat with the ability to override the car?

These are questions that there aren’t answers to yet. In February the National Highway Traffic Safety Administration in some way told Google that the self-driving system they have in place could be considered a driver under certain regulations that currently exist. But that wasn’t carte blanche to start production. It was one interpretation.

Another obstacle in that same vein is how states will view the cars. Each state has its own driving restrictions and licensing. That may mean that self-driving cars are only available in particular states to start. If that’s the case, are cars allowed to cross state lines in the same ways that cars with different regulations in one state can currently drive in other states?

There are a lot of exciting developments happening with self-driving cars. The technology is evolving rapidly and in a way where pieces of it are entering vehicles already. However, there’s a long way to go and many things yet to discover and sort out. Nonetheless, it’s an exciting time in cars, with the automobile about to enter a completely new era.