Photo by dimic- on Flickr.

Google revealed this week that it is working on autonomous cars, and making a lot of progress. While it’s what engineers call a nontrivial problem, making a car drive itself is ultimately just a matter of engineering, and will sooner or later become a reality.

What will it mean for our cities? Will cars that drive themselves lead to more driving or less? More sprawl or more compact living?

On the one hand, long commutes will become more tolerable. Instead of suffering behind the wheel for hours, commuters who live far from their jobs will at least be able to get some work done or watch TV. This could make distant exurbs a bit more appealing and boost sprawl.

It will also probably cut down on commuter rail ridership, since some people choose rail over driving because they like not having to actually drive. However, even a small increase in vehicle volume will bring many freeways to a halt, making commuter rail more attractive time-wise, so it’s not likely to have a large effect.

But the biggest change will be autonomous buses.

Today, buses have fairly high operating costs because of the labor involved. They’re far more space-efficient than cars, but it’s expensive to pay a driver. The biggest reason transit costs more to operate than highways is because with transit, you’re paying a driver, but if you’re driving your own car, you’re doing the labor yourself.

That’s a structural imbalance that puts transit at a budgetary disadvantage, until your car drives yourself and so can the bus. Suddenly, there’s no difference.

Cities with self-driving trains, like Vancouver, can run far greater frequency at low ridership times like nights for a reasonable price. More vehicles makes transit more appealing.

Now, buses are often very infrequent or nonexistent at night, making them an unappealing mode for an evening trip, for example, unless you live right near a high-frequency, late night line. But what if the bus just drove itself every 5 minutes? Basically, it’s like everything PRT promises, but without any guideways.

Or, better yet, what if it ran on demand? Then it’s like a cheap taxi. And, in fact, buses, taxis, and car sharing will essentially merge into one mode.

Right now, each of those modes has advantages and disadvantages. Buses have the labor cost issue. Taxis have it even more, but are very convenient when available. Car sharing is great for certain types of trips, but you have to return the car to its starting point.

With autonomous vehicles, there will be no need to differentiate between vehicles that carry many people on fixed routes (buses), vehicles that carry few people on demand (taxis), and vehicles you can drive but are only in certain places (car sharing).

Instead, you’ll simply be able to call a number or use a mobile app to book a trip. In urban areas, you’d go to a designated bus stop, or maybe pay more to get a custom pickup right where you are. A vehicle will show up at an assigned time, maybe picking up a few other people as well who are going to a similar destination, unless you want to buy a solo trip.

For more on how this could work, see Mark Gorton’s Smart Para-Transit articles.

We’ll need far fewer parking spaces in dense areas. Commuters from suburbs that take autonomous buses/taxis/paratransit vehicles/car sharing cars into the city won’t need to park them. Instead, they can drive themselves around all day serving short-range trips as taxis. Others would live in the city full-time, and those might need overnight parking, but far less than we have today.

It will simply become far easier and cheaper to live in the city without a car. It won’t really be like living without a car today. It will simply be like living with a car, without worrying about parking or paying nearly as much. Or, perhaps, it’s like using car sharing, but with the guarantee that a car is always available and without having to worry about getting the car back in time.

Finally, assuming Google can perfect the software, streets will become much safer. The cars will be far better at avoiding crashes. Instead of most drivers speeding, turning improperly across bike lanes, and being distracted with texting or phone calls or the radio, the car will be “paying attention” at every moment (as long as its software isn’t buggy!)

Governments and manufacturers will have to decide how to handle speed limits. Today, many localities set speed limits knowing most people speed. Will drivers be able to choose their speed, or will cars be required to travel the actual speed limit? If so, maybe we can finally rationalize all these limits and set them appropriately.

If governments set up autonomous car-only lanes on freeways or ban human-driven cars altogether once most cars drive themselves, traffic can move more efficiently. Right now, if a bunch of cars are stopped in traffic or at a light, each driver has to wait a few seconds after the car in front starts moving. With computers, the entire line of cars could simply start moving all at once.

The greater efficiency will allow existing freeways to carry more people than they do now, and since it’ll be a lot easier to create carpools with Smart Para-Transit dispatching, even more if jurisdictions are willing to convert lanes to HOV. That could also accelerate sprawl, but the greater ease of urban living and lower need for parking will also facilitate infill development as well.

How else will cities change if cars can drive themselves?

David Alpert is the founder of Greater Greater Washington and its board president. He worked as a Product Manager for Google for six years and has lived in the Boston, San Francisco, and New York metro areas in addition to Washington, DC. He lives with his wife and two children in Dupont Circle.