When should car buyers -- and investors -- expect driverless vehicles to be available to the public?

It's a question I get asked all the time. That's no surprise: Self-driving vehicles are likely to be a transformative technology, and we Fools love to get in on those early on. 

But it turns out that the answer to the question depends on what you mean by "driverless" -- and by "available." 

A white Chrysler Pacifica Hybrid minivan with Waymo logos and visible self-driving sensor hardware is shown driving on a street in Chandler, Arizona, earlier in 2017.

Waymo, the company formerly known as the Google Self-Driving Car Project, is a leader in the driverless-car race. But it's not yet clear how Waymo will bring its technology to market. Image source: Fiat Chrysler Automobiles.

What we mean by "driverless" cars

First, let's define some terms. "Driverless," "autonomous," and "self-driving" all mean pretty much the same thing: a vehicle that can drive itself with no human intervention required, at least under some circumstances.

There's nothing like that on the market quite yet. While systems like Tesla's (TSLA -3.65%) Autopilot and General Motors' (GM -0.73%) Super Cruise do allow hands-free driving under limited circumstances, both require the presence of a human driver who is at least somewhat alert and ready to take over the task of driving on short notice. 

SAE International, the professional association of automotive engineers, defines vehicle automation in six steps, from Level 0 (no automation) to Level 5 (full automation). You can learn more about the "levels" here, but for our purposes, Levels 4 and 5 are the ones that are effectively "self-driving."

What's the difference? Level 4 is full self-driving within certain limits: Most of the self-driving systems likely to come to market in the near future are dependent on highly detailed 3-D maps; if you want to go somewhere that isn't on the car's map, you'll have to drive yourself. There may be other limits as well: A Level 4 system might not work in the snow, for instance. 

2 Ford Fusions with visible self-driving hardware are shown testing on a snowy road.

Snow and ice present big challenges to driverless-vehicle systems. Image source: Ford Motor Company.

Level 5 is a system that can drive anywhere a human driver could. The driverless-car systems likely to come to market in the near future are Level 4, limited to mapped areas. As the maps expand over time, those vehicles will come closer and closer to Level 5. But most experts think a full-blown Level 5 system is at least several years away. 

To sum up: For at least the next several years, driverless vehicles will be "geofenced," limited to areas that have been carefully mapped. They may also be limited by weather and other conditions.  

But Level 4 vehicles are coming soon. To understand how soon, let's look at how they're likely to come to market.

The race to develop a driverless car has many contenders

There are a number of efforts underway to bring a Level 4 system to market in the near future. Among the most prominent: 

  • Delphi Automotive (DLPH), Intel (INTC -1.99%), and Intel subsidiary Mobileye have promised to make a Level 4 system available to automakers by the end of 2019. Vehicles using that system could come to market by 2021 or so.
  • Those partners are involved in a separate-but-related effort with BMW AG, Magna International, and Fiat Chrysler Automobiles that aims to bring a self-driving technology "platform" to market by 2021. 
  • Swedish automaker Volvo Cars and auto industry supplier Autoliv have formed a joint venture that is also aiming to bring a system to market by 2021. It'll be used by Volvo in its own cars, and marketed to other automakers by Autoliv. 
  • A slew of automakers and technology companies have their own efforts in progress, including Alphabet's (GOOG 0.80%) (GOOGL 0.78%) Waymo subsidiary, GM, Tesla, Volkswagen AG, and Ford Motor Company

But note: The answer to the question in the headline isn't necessarily going to be "2021." Although there are many development efforts underway, the first Level 4 cars to come to market probably won't be sold directly to consumers. Instead, they'll be put into service with ride-hailing companies like Uber Technologies and Lyft: They'll be automated taxis, limited (at least at first) to well-mapped cities.

A white Chevrolet Bolt EV with Cruise Automation logos and visible self-driving sensor hardware is parked outside GM's historic Design Dome in Warren, Michigan.

A Level 4 driverless version of GM's Chevrolet Bolt EV may become the first mass-produced driverless car, within two years. Image source: General Motors. 

Several U.S. cities have already been well mapped, including Pittsburgh (home of Uber's own self-driving technology program) and San Francisco, home of GM's self-driving subsidiary Cruise Automation. GM said recently that it is currently working to map New York City and other mapping efforts are under way around the country. 

When will that start to happen? GM expects to have Level 4 vehicles operating in ride-hailing service in dense urban areas at scale by 2019. Waymo may be thinking along similar lines: It recently took a big step in that general direction, announcing that some of its test vehicles operating in Arizona will soon begin testing without a human driver standing by at the wheel. 

So when will self-driving cars show up at dealerships? 

So when will we be able to buy one? That may turn out to be a question for regulators, and the answer may depend on how well the first Level 4 vehicles perform in ride-hailing service. If they have a lot of problems, it'll take longer. 

It may also depend on the public's reaction: How many people will want the technology on their privately owned vehicles, and how much will they be willing to pay for it? (Of course, a few companies -- I'm thinking of Tesla here -- might not wait to find out what regulators or the public think.)

Long story short: Assuming there are no legal obstacles, the first cars with Level 4 systems could start to show up at dealerships within a couple of years, but it may take longer. Either way, it's likely that you'll be able to ride in one before you can buy one, by 2019 if not earlier. And it's also likely that full-blown Level 5 vehicles are still many years away.