In the future, you won't be buying cars. You will be subscribing to 'Goober'.

Steve Tennison's Tesla cruises on autopilot down the Southwest Freeway.

"I find I speed less when autopilot is on," says Tennison, his hands at his side and feet off the pedals as his 2015 Tesla Model S 85D glides down the Westpark Tollway.

Americans are already sharing the road with self-driving cars. This technology may have a profound impact much faster than expected - especially on cities like Houston, with multiple centers spread across a huge area.

Early adopters like Steve open a window into the near future.

The trip in the Tesla begins in Montrose on a Saturday afternoon. A storm has just cleared, and the January sun on my face feels good. While fiddling with the audio recorder on my phone, I don't notice that Steve has turned on the autopilot feature. With trucks and cars all around us, the Tesla passes deftly through the grand columns of the 610 interchange.

The steering wheel turns itself, which is spooky. The dashboard display shows an approximation of what the Tesla detects using cameras, radar, ultrasonics and GPS. Lanes and nearby vehicles are highlighted in blue.

The car changes lanes on its own or with a tip of the turn-signal lever. Steve takes control to get on the ramp to the Westpark Tollway, which the Tesla autopilot then handles with ease. Steve is attentive and ready to grab the wheel at any moment. We follow the route of his office commute. Near his office, Steve demonstrates the car's ability to parallel park on its own.

On a quiet road, he turns off autopilot and then floors it. The standard Model S can hit 60 in about five seconds; my stomach is 50 feet behind me somewhere in the middle of the road. I really prefer the ride when the autopilot is left on. Maybe I should have asked Google for a ride in Austin, where it is testing its car at speeds no higher than 25 miles per hour.

Then Steve lets the Tesla try to navigate the complexities of Westheimer. We trail a Metro bus. The ride is remarkably smooth in stop-and-go traffic.

Transformative shifts

In "Beyond Google's Cute Car," an article published in "Cite: The Architecture & Design Review of Houston," landscape architect Kinder Baumgardner argues that the "transformative effect of autonomous vehicles on non-antique cities - the 'Houstons' of the world - will be especially profound. The debate about designing for an autonomous vehicle future needs a jumpstart: How will they shift the basic economics of land use? And what are the design implications?"

The biggest consequences for the city might not be on the roads. Steve's Tesla, for example, not only parallel parks on its own, but it can drop him off at a front door and then park itself in a distant garage. (Currently that feature works only on private land.)

In the future, Houston buildings with front doors that face parking lots could be reoriented to the street. And city ordinances that require minimum parking allotments depending on building use might need to be revisited. (Under today's law, for example, bowling alleys must have five parking spots per lane.)

Baumgardner envisions even more transformative shifts.

"After the marriage of autonomous vehicles (Google) and app-based car sharing (Uber), you will be subscribing to Goober, not buying cars," he writes. "You will need less space to get where you are going, and no space to park the car."

Baumgardner and a team at SWA Group - the landscape architecture, planning and urban design firm where he serves as president - imagine what will become of downtown Houston's roughly 100,000 parking spaces. A 10-story parking garage may only have cars parked on the first few floors, leaving the rest of the space open for creative reuse. As fewer parking spaces are needed, many businesses won't be required to provide parking, and "we will see an explosion of restaurants, bars, coffee shops, and other experiential retail that Amazon Prime Now cannot deliver to your door."

When Steve pulls the Tesla up to his house in Montrose, the garage door opens on its own. Of course. The Tesla knows. It even automatically adjusts the suspension so the bumper doesn't scrape.

I have no idea how fast self-driving vehicles will make their way into the average person's life. It could start with ultra-cheap buses plying the most boring highways. Perhaps we will be able to rent cars that travel in caravans overnight to Marfa.

But this much I know: Big changes are not far down the road.