The technological pieces of self-driving, self-charging, electric vehicles are quickly falling into place.

As these vehicles inch tantalizingly closer to reality, we are starting to imagine an entirely new transportation system, in which self-driving electric vehicles are organized into shared city fleets, and dispatched by smartphone to satisfy transportation demand. In this brave, new world, there’s no need for private vehicle ownership.

Yet, while we can envision a safer, more livable utopia, we can also imagine a dystopia, clogged with yet more cars and congestion. We know huge, fundamental transformation is coming to our transportation system, but it remains maddeningly difficult to predict exactly what shape those changes will take.

Our transportation system has not changed much, except to become bigger and more sprawling, in over 60 years. There are so many moving pieces today, so many new technologies and possibilities, that it seems impossible to wrap your head around what may be coming.

One way to think about it is this: Technology is enabling a shift to self-driving vehicles, a shift to electric vehicles, and a shift to shared vehicles. Each of those shifts will have its own effects. It can be helpful to try to disaggregate those effects.

That’s what a recent study from the International Transport Forum (an OECD think tank) attempts to accomplish. In particular, it tries to focus in on the sharing part.

ITF actually did a separate report last year on shared fleets of self-driving cars. It built on extensive travel survey data to create a simulation of motorized travel in the streets of Lisbon, Portugal (a fairly representative mid-sized European city), and ran various models on that simulation.

For this new study, they’ve used the same simulation, but the vehicles being modeled are not electric or self-driving; They are internal combustion vehicles, designed for common use. That way, it’s easier to isolate the specific benefits of sharing.

It turns out the benefits of shared vehicles are potentially staggeringly big: Fewer vehicles on the road, fewer vehicle miles traveled, far less need for parking, lower pollution and carbon emissions, and radically increased access to jobs, health care facilities, and schools. Join me on a stroll through them.

The way we use cars now is dumb

Let’s take a step back, and consider two key facts about privately owned cars:

1) they’re parked about 95 percent of the time, and

2) more than 70 percent of commutes in most US cities are in single-occupancy vehicles (SOVs).

Most cars sit around most of the time, and when they run, they carry one person. That represents a grotesquely inefficient use of resources. As a result, our transportation infrastructure is radically overbuilt for what we need. We have too many cars and too much parking.

And it’s gotten us, as ITF summarizes, "environmental impacts, loss of transport system efficiency due to congestion, social inequity and exclusion, as well as road crashes and strong dependence on fossil fuels."

Why do we put up with all this? Because the private car, ITF writes, "presents a clear advantage over other transport options in three key areas: flexibility, comfort and availability." You can take your car wherever you want, whenever you want, in privacy and comfort. It has proven very difficult for public transportation to reverse or even slow the trend to SOVs.

What if we could put cars to use more of the time and carry more people in them? It stands to reason that we’d need fewer of them. That’s the promise of shared vehicles.

Coordinating vehicles better addresses multiple problems at once

Thanks to developments in IT, we now have the technology — the sensors and software and GPS — to better coordinate vehicle use in cities. And coordination works best with shared vehicles.

So ITF models a system that uses shared vehicles. Specifically, there are two fleets.

The first and larger is "a ridesharing system (shared taxi), which emulates a taxi-like system where customers accept small detours from their original direct path and share part of their ride with others." This would more or less be like how companies like Uber and Lyft operate, but would a) pick up other passengers on similar routes, b) be controlled by a central dispatch (more on that central dispatch later).

(Worth noting: Uber already has UberPool, which allows, but does not mandate, shared rides.)

The second is "a dynamic bus-like service with minibuses (Taxi-Bus), where customers pre-book their service at least 30 minutes in advance … and walk short distances to a designated pop-up stop." The idea is that these small (eight or 16 seat) minibuses-on-demand would mostly run on regular commuting routes, but would be flexible enough to shift with evolving demand.

The two fleets are meant to "fully replace current motorised road transport alternatives (car, motorcycle, taxi and bus)," while leaving high-occupancy, fixed-route transit options like subways and trains in place. The goal is to use vehicles more efficiently but preserve the "levels of comfort and flexibility normally associated with the private car."

So what happens if all of a city’s personal transportation needs are met by such a system? The detailed results are worth reading, but the ITF summary of the model results is pretty stunning:

Congestion disappeared, traffic emissions were reduced by one third, and 95% less space was required for public parking in our model city served by Shared Taxis and Taxi-Buses. The car fleet needed would be only 3% in size of the today's fleet. Although each car would be running almost ten times more kilometres than currently, total vehicle-kilometres would be 37% less even during peak hours. The much longer distances travelled imply shorter life cycles for the shared vehicles. This enables faster uptake of newer, cleaner technologies and contributes to more rapid reduction of CO2 emissions from urban mobility. Citizens gain in many different ways. They no longer need to factor in congestion. Almost all of their trips are direct, without need for transfers. Mobility is much cheaper thanks to the highly efficient use of capacity; prices for journeys in the city could be 50% or less of today even without subsidy. Huge amounts of space previously dedicated to parking can be converted to uses that increase livability, from public parks to broader sidewalks, and more and better bicycle lanes. Particularly striking is how a shared mobility system improves access and social inclusion. In the simulation, inequalities in access to jobs, schools or health services across the city virtually disappeared.

Almost every sentence of that is crazypants. Vehicle emissions would drop by a third! (And that’s with gas cars, not electric.) The car fleet would only need to be 3 percent the size of today’s! Total miles (er, kilometres) driven would fall by 37 percent! That’s a city with fewer cars on the road, more space to work with, and cleaner air.

The improvement in access is also noteworthy. Here’s a visual showing how access to jobs would increase:

The results for access to health and education facilities are similar — they become virtually universal after the change.

That’s a really big deal. For one thing, distributing access to key services via the lottery of who can afford a car and centrally located housing is intrinsically inequitable. For another, better access to jobs, health, and education is not just a boost in social justice, it’s a huge economic driver. It puts human resources to better use.

From these results, shared vehicles look like an unqualified win, economically, environmentally, and socially.

Shifting these shared, centrally dispatched vehicles to self-driving electric vehicles would expand all these benefits (read this Tim Lee post on that subject), but it is nonetheless striking to contemplate what could be done with smart sharing alone.

Getting to shared vehicles is tricky, to put it mildly

There are a million caveats here, obviously. This is only one model of one city; every city has different geography, density, and traffic patterns. And the scenario it describes — replacing all private vehicle travel in one fell swoop — is wildly unrealistic.

The transition, getting from private vehicles to shared vehicles, is the most difficult part. ITF notes that the real benefits of sharing don’t really kick in until the private vehicle fleet has shrunk by at least 60 percent. How would such a system get started? There’s no demand for it until it exists. It’s a classic bootstraps problem.

ITF discusses the possibility of banning private vehicles in the city one or two days a week at first, just to demonstrate the desirability of the alternative. I’m having a little trouble envisioning that working out, having two fleets operating side by side on different days, but maybe some small European city is crazy enough to try it.

Needless to say, the social and logistical challenges of swapping one fleet of vehicles for another are, as yet, only dimly understood and highly unlikely to be smooth sailing.

Another big question relates to the central dispatching authority, the one coordinating the movements of these hundreds or thousands of vehicles. If it has a monopoly on urban dispatch, is it a public utility? A contracted private company? Who is responsible for determining the rules and algorithms that govern dispatch?

Car sharing is part of the larger clean energy transition

Nonetheless, despite its highly speculative nature, I think this study reinforces a few things.