If the enthusiasts are to be believed, driverless, electric cars will augur the end of all of humanity’s traffic woes. With nifty “mobility-on-demand” at our fingertips, we will live in cities that — as one autonomous driving start-up imagines — have “no congestion, zero traffic fatalities, instant parking available on demand, safe routes for cars, bikes and pedestrians and modern, efficient, up-to-date infrastructure.”

There sure is a lot of hype around autonomous cars. Tech firms love the concept — the vehicle is a mobile IT platform like no other. By and large, journalists and other commentators have been happy to go along for the ride. Who doesn’t want to live in a future free from congestion, collisions, and pollution from combustion engines and the petroleum supply chain?

The truth is that autonomous cars do hold huge potential to make cities more safe and sustainable — but only if they are introduced in the right way. Huge real-world challenges still exist to the wide adoption of the technology, but let’s say for a moment we get all this working, and our cities become flooded by driverless vehicles. As for any powerful new technology, we must ask ourselves: What could go disastrously wrong? What are some of the key vulnerabilities of such a new system? What are the nightmare scenarios of a driverless future?

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Through the Rocky Mountain Institute‘s work with carmakers, technology firms, urban planners, and policy makers, I have identified five threats to autonomous driving — with a focus on the U.S. — that I hope adds diverse and contrarian thinking to discussions of a driverless future. I list them in rough order of immediate impact because some will be sudden and calamitous, and some will be more insidious, only becoming obvious over time. And I offer a few preliminary thoughts about potential solutions.

System Meltdown

The threat: Autonomous driving will rely on a digital information backbone to operate. Experience clearly shows that such infrastructure systems have a far from perfect — or even close to perfect — record. The U.S. electricity grid, for example, is one of the largest and oldest and is famously insecure. It has constant weather or equipment-failure driven shutdowns. That’s not even taking into account the threat of cyber-attack that any autonomous driving system will have to stay ahead of.

The Fix: More modern systems and architectures can theoretically do a much better job of preventing or at least isolating issues, so a system-level shut-down becomes technically impossible. This could also apply to protecting our electricity systems from hackers.

Public Panic

The threat: What happens if a well publicized event like a terrible accident reveals a fundamental flaw in the system? Will the public tolerate early failures? Though nasty accidents will be rare, it is still quite likely that odd combinations of events will permit them to occasionally happen, and today’s press, pundits, and politicians are hardly to be trusted to wait for the unwinding of a causality to weigh in — and their emphasis on truth might also be doubted. As for any transportation system, trust is essential.

The Fix: In such a data-rich environment the most egregious exaggerations and falsehoods can be easily — and perhaps visually and vividly — disproved. Highlighting the many system benefits will likely cause the public at large to be supportive — especially when they are reminded that they already tolerate the dangerous and inefficient systems we have today.

Endless Errands

The threat: What happens if people flood the system by sending driverless cars out on constant, frivolous errands? This problem, and its variant, endless deliveries (by commercial players) is a brain teaser, because of the way the flow of goods actually shapes the systems that provide them, and the behavior of the users. They also shape the physical landscape.

The fix: It is not clear how big a problem this could become. If consumers have more time when they are not focused on driving or worrying about traffic, they are likely to do a better job of not forgetting the eggs. Errand businesses may spring up that effectively consolidate the errands. Cities may also be able to provide a gentle deterrent to driverless car abuse by switching road maintenance funding to usage-based fees, a step which is important to bring about anyway because the current fuel-based system no longer measures driving (and usage) effectively.

Car-lovers revolt

The threat: Some people love cars. Others don’t. Can car-owning enthusiasts “wreck” the system by effectively resisting car sharing or insisting that they be allowed to drive anywhere, anytime? Could they claim an analog to the U.S. Second Amendment and argue that their freedom of movement by automobile is inalienable? This would significantly reduce overall system efficiency and savings — a huge social cost, in order to preserve a so-called individual freedom. But it’s also hard to imagine forcing people to use driverless technology; the best we could hope for would be offering carrots like express-lane access.

The fix: This is a threat that democracy should be able to resolve — but it will be incumbent on policy makers to roll-out autonomous driving where the benefits are the greatest and then share the results widely and vocally. Car lovers should be given some fun places to play. A (hopefully diminishing) set of non-sharers should have an appropriately more expensive option. While having some people opt out can be tolerated, the goal should make sure that they do not mess up the highways the rest of us really need – to the workplace or the school or the shopping center.

Benefit erosion

The Threat: Because a driverless future will require totally new systems, there will be many interdependent features in the overall design, such as the number of cars, the mix of electric versus conventional vehicles, the amount of car-sharing, how effectively personal transport is linked with mass transport, and others. If some of the features get changed a bit too much, modeling indicates that overall benefits — like lower congestion levels and lower cost of transportation overall — rapidly diminish. And without those clear benefits, societal acceptance of change will be much tougher, if not impossible. There are many incumbent players with huge power in the existing transportation status quo that may push for accommodations – examples include continued provision of excess parking at public cost (which discourages car sharing) or continued tax incentives for businesses to own rather than share vehicles. There is a chance that such compromises may add up to a poor solution that doesn’t really work, leaving us with a new kind of mess on our hands that is no better, cleaner, or safer than the current one.

The Fix: This is perhaps the most dangerous threat. There is no way to ensure that accommodations not be made — designers will just have to do their best to truly understand ahead of time what the key sensitivity points are and push like crazy to avoid the false compromises that endanger the overall promise of driverless technology – while being reasonable about everything else.

I welcome a future dominated by driverless cities and suburbs — but I’m cautious. We do have one fundamental advantage when it comes to pushing this attractive set of innovations to reality — there are a lot of cities. Each city can experiment, share learnings and narrow down the set of workable solutions quite rapidly. That doesn’t sound like a utopian dream to me. It sounds a lot like how science, progress — and maybe even politics — should be done.