There was a time when manual transmissions always outperformed automatics on the track, but you won’t find a clutch on today’s F1 supercars anymore. Those have been replaced by semi-automatic paddle shifters mounted to the steering column. Even on the street-legal consumer side, acceleration is a shifting landscape. While six-speed manuals such as the Lingenfelter Chevy Corvette and Dodge Viper Hennessey Venom still hold the top 0 to 60 mph times, today’s automatics are increasingly accelerating faster and getting better fuel economy than their manual counterparts in what amounts to a significant changing of the guard.

In the automotive world—as in computing, Jeopardy!, and sometimes even chess—technology is outperforming humans.

With much talk about driverless car technology lately, that begs a number of questions. One example: Vehicle fuel efficiency, hybrids, and electric vehicles are central to a transforming, cleaner, greener transportation system; What will driverless cars mean for fossil fuel consumption in the transportation sector? (See related post: “Google Gets First Driverless Car License: Strings Attached.”)

Individual driverless cars come with important opportunities for increased efficiency. Groups of driverless cars likewise have the potential for even greater collective efficiencies, for example through shared reduced drag. And driverless vehicles seamlessly connected to smart infrastructure offer even greater promise still.

Consider hypermiling, which focuses on maximizing fuel efficiency through driving technique and has a cult of devout enthusiasts pushing the limits of their vehicles’ mpg. For example, one driver on hypermiling site is coaxing more than 86 mpg out of a 1988 Honda Civic, besting its EPA rating by close to 175 percent.

Hypermiling requires a whole new approach to driving—how fast you drive; how you accelerate, brake, and approach hills and traffic lights. Most drivers aren’t well versed in how to hypermile; they just try to maintain (or not overly exceed) the speed limit. But driverless cars could do the hypermiling for us. (The Honda Civic Hybrid’s Econ Button is already a small step in that direction, prioritizing efficiency over a driver’s lead foot tendencies.)

And while hypermiling is often derided as “a fun way to drive slow,” driverless cars—via connected autonomy—could actually enable us to get places faster while still maintaining hypermile-like fuel economy. (See also: “Smarter Trucking Saves Fuel Over the Long  Haul.”)

There’s a memorable scene in Days of Thunder when a young Tom Cruise teaches Nicole Kidman the concept of drafting: “When one car tucks in behind another, two cars go faster than one. They divide the air resistance between them. Now here’s where it gets interesting. The lead car has to floor it to hit 200 mph, but the car that’s tucked in behind doesn’t. It can go just as fast and still have power in  reserve.”

In the context of driverless cars, drafting becomes platooning, a grouped “train” of autonomous, connected cars following a lead car. The SARTRE project—fully operational today and potentially ready for consumer deployment within 10 years—is the latest iteration of a concept that first gained popularity in the 1990s. By traveling within 13 feet of one another, the platooned vehicles reap great efficiency gains. A 1995 PATH (Partners for Advanced Transportation TecHnology) study showed fuel use reductions up to 20 percent at this distance; even greater reductions are possible with larger platoons and/or tighter spacing between vehicles.

Now here’s where driverless cars, hypermiling, and speed all potentially intersect. The National Highway Maximum Speed Law of 1974, motivated by the 1970s oil crisis, gave us the 55 mph speed limit, targeted at keeping U.S. drivers at peak fuel efficiency. In 1995, the law was abolished and speed limits now vary widely state by state, though 55 mph remains common on many of the nation’s highways. But what if driverless cars—by being able to safely maintain much closer following distances in platoons than human drivers—could actually increase the speed of peak efficiency? We’d get places faster while still using less fuel.

The opportunities bound up in driverless cars are many. They’re highly compatible with car-sharing programs (more on that in a future post). They have implications for public transportation systems (ditto). If you’re feeling drowsy on a long-haul drive or at the end of a tough day at work, a driverless car could let you sit back and relax, or even take the wheel if it senses you’re driving erratically; ditto if you find you’ve unexpectedly had too much to drink—rather than call a taxi, a driverless car could take you home. By feeding information into (and obtaining info from) a shared database akin to the smartphone app Pothole Alert, they could avoid road hazards or even notify the local highway department or department of public works to road repair and maintenance needs.

But let’s return to the fuel consumption issue. Driverless cars connected to the traffic light system could communicate with an upcoming light and have it stay green or change to green, so that you could maintain cruising speed and optimal fuel efficiency (not to mention avoiding an unnecessary delay at the light). And of course there’s the familiar issue of parking, especially in urban environments where it accounts for 30 percent of all traffic. Autonomous cars and a smart parking system could allocate parking spaces to the nearest vehicles in need of a spot, and vehicles could navigate to those spots directly and quickly, reducing the fuel consumption, emissions, and time associated with searching for a spot.

There are pitfalls to be wary of, however. One giant elephant in the driverless car room is vehicle miles traveled (VMT). It’s tempting to believe that driverless cars will reduce VMTs through various efficiencies, but the opposite could also happen. In a highly autonomous vehicle future, we may do far more with our cars than we currently can—think of Pierce Brosnan’s James Bond calling his BMW 750 via cell phone in Tomorrow Never Dies, or David Hasselhoff’s Michael Knight and his autonomous car, KITT, each chasing down different suspects in Knight Rider.

What if our driverless cars of the future have a valet mode that allows them to park themselves, becoming not just driverless but also passengerless? What if they run errands for us, such as picking up lunch or dry cleaning or the kids at soccer practice? What if driverless cars—and the efficiencies and flexibility they offer—actually incentivize us to drive more? This “rebound effect” could increase VMT and fuel consumption, eating into the potential energy savings we’d otherwise expect from highly efficient autonomous vehicles. We must be prepared to address these undesirable yet entirely possible outcomes.

Robert Frost wrote, “Two roads diverged in a wood, and I— / I took the one less traveled by, / And that has made all the difference.” With the dawn of driverless vehicle technology, we are at a fork in the road, each path with its own consequences, positive and negative. Driverless vehicle technology can and likely will make a difference. But what difference will it make? It has the potential to be radically more efficient than the status quo, but it also might increase—possibly substantially—VMTs and fuel consumption. So how do we ensure that our future state is more of the former, and less the latter? We’ll explore that in coming posts.

—Roy Torbert & Blake Herrschaft

This post originally appeared at the RMI Outlet and was republished with permission.



  1. Concerned
    February 9, 2013, 6:49 am

    Well, if we used electric vehicles instead of the old fashioned ones we drive today, we could greatly reduce the amount of fuels burned! TA-DA!

  2. John Grannis
    New Jersey, USA
    February 9, 2013, 3:11 am

    I’m all for more fuel efficient cars, and more locally organized communities to promote walking and biking. But I will not gladly surrender my personal autonomy, ie. my freedom. I suspect most people feel the same way. Personal freedom is what driving is all about, not some engineer’s notion of optimal transportation efficiency. Let’s not make people obsolete!

  3. Roy Torbert
    Boulder, Co
    February 7, 2013, 5:00 pm

    Excellent point from Neil, one advantage of driverless cars is their suitability for a taxi service or car-sharing program. And once we’ve reduced the total number of personal vehicles through other forms of safe and easily available personal mobility, we certainly might see far more urban planning focused around pedestrians.

    And Fx – you’re right that driverless cars can be much lighter, though I’d expect those that hold passengers will still need to offer heating and air-conditioning. From the perspective of the entire transportation system, we would be much much safer and more efficient if our 2-ton cars could go on a diet.

    The issue of liability is enormous. When a driverless car gets in an accident – is the driver liable? Or the auto manufacturer? Or the software provider? We certainly can’t afford a major investigation of all these parties for every incident. These are central questions, determined partially by the technology, but also by policy and regulators. This new technology is moving quickly, and we’re cautiously excited about what it might bring!

  4. Fx
    February 7, 2013, 2:39 pm

    A driverless car could also be lighter (much in the way drones are lighter than conventional planes). You could strip out the weight of the driver & passenger safety features, the cabin heating and air-conditioning systems, etc., which would help improve fuel-economy.

    But — and it’s a big but — the liability considerations are staggering. I suspect that juries would tend to hand down judgements in favor of human drivers vs. driver-less vehicles, despite being presented with mountains of safety and test data.

  5. nolan
    February 7, 2013, 12:06 pm

    I think it could help because the weight of the american people can cause Fossil Fuels to burn faster

  6. neil21
    February 6, 2013, 2:05 pm

    That’s why I prefer the term e-Robotaxi. Since cars sit idle most of the time, and since remembering the charge them is the biggest remaining annoyance of EVs, I assume robotaxis will be the killer app for EVs. Go charge themselves, and mark as unavailable on my cab-hailing app, when necessary.

    And regarding VMT, undermining personal vehicle ownership is the key to demand for walkability retrofits. If a suburbanite owns a car, she’ll lobby against wider sidewalks at the expense of roadspace. If she doesn’t, she’s more likely to be in favor of a pleasant walk to a local store.

  7. Flyguy
    February 6, 2013, 12:00 pm

    It could have its pros and cons, what would happen if you got into a wreck?


  8. V-man
    February 6, 2013, 11:55 am

    If it works, saves fuel, and saves money, try it, it can’t hurt

  9. FrogLady
    February 6, 2013, 8:40 am

    “…a driverless car could let you sit back and relax, or even take the wheel if it senses you’re driving erratically…”

    Which means that a remote operator could also sieze control of my car as well. Government, yes, but also hackers. Despite the illusory “security” of technologies, system hacking happens more frequently than most people suppose. No thank you!