Otto's self-driving truck. Otto Self-driving cars are coming.

Tesla is aiming to have a fully driverless car ready by 2018, and Uber recently kicked off a pilot in Pittsburgh where select users can hail a ride in a self-driving car. And many other companies have plans to roll out some form of self-driving cars by 2020.

But chances are, you're more likely to see a driverless truck in practice before a self-driving car.

There's two reasons for this, the first being the tech itself.

It's a lot easier to build autonomous tech for highway driving than city maneuvering. On highways, there are fewer obstacles for the vehicles to worry about. Cities are a mess of pedestrians, cars, potholes, traffic cones — you get the point. All of those obstacles mean driverless cars have a lot to keep track of, and it can be easy to miss something.

We've already seen real world examples of this playing out. Uber's self-driving cars still need a safety driver behind the wheel because urban driving is so difficult. There were actually several times the driver had to take over when we got a ride in one.

A depiction of Tesla's Autopilot in use on a highway, Tesla

But there are already vehicles on the road today that can handle highway driving with relative ease. Tesla's Autopilot comes with the ability to merge on and off highways, detect when another car is entering your lane, and drive in highway traffic.

It's not just Tesla, either. Most cars today come with semi-autonomous features for highway driving, like the Volvo XC90, which comes with Cruise Control and Pilot Assist so the car can drive itself even on traffic-heavy highways.

That's not to say vehicles are completely able to tackle highway driving on their own yet. Otto, a self-driving truck startup that Uber bought for an estimated $680 million, still needs someone behind the wheel in case something happens.

YouTube/Otto

But Business Insider's Biz Carson got a ride in an Otto truck and wrote that it handled the highway so well it "for the most part, felt normal — relaxing, even." There were no chimes indicating the need for a driver to take over during her ride as was the case with Uber's self-driving cars — but again, it's much easier to handle an open highway than a chaotic city.

But it's not just the tech itself — it also makes more economic sense to pursue driverless trucks.

The Center for Technology Innovation at Brookings put together a report noting that delivery vehicles and trucks are poised to see "quick adoption of autonomous vehicles" because e-commerce is booming. People are increasingly likely to order food and goods online with the promise of same-day delivery, which has served as a boon to the trucking industry.

Now if you consider that large trucks often cost over $150,000, then the introduction of autonomous tech, like cameras and sensors, begins to seem "quite cost effective compared to the case with automobiles, where the additional expense is based on a lower overall cost," the report notes.

So as more money is getting poured into delivery systems, the prospect of investing in autonomous tech for trucks now — with the idea that it will cut costs later — becomes a more attractive prospect.

Daimler's autonomous truck. Daimler

We're already seeing a movement toward driverless truck adoption. In addition to Otto, Daimler is working to get its driverless truck on the road by 2020. The truck made history by driving on an open highway with traffic October 2015, marking the first time a big-rig drove semi-autonomously on a highway.

And it's possible other companies investing heavily in delivery networks will look to driverless trucks in the future as well.

Deutsche Bank released a report in June predicting that Amazon will have a shipping operation that consists of self-driving trucks and drones. Considering Amazon has invested heavily in growing its transportation network over the last few years, that doesn't seem like a stretch.

There's an immense focus on self-driving cars right now, and with good reason. Driverless cars can improve congestion and traffic while decreasing the number of accidents. But having so many hurdles to overcome still, it seems most likely we will see a driverless truck first.