Three important and interrelated questions being asked about cities and cars today are:

  1. How can we create more livable and sustainable communities with a more intelligent mix of mobility modes including walking, biking, transit use and planning such as Complete Streets?
  2. How can we reduce the environmental harm generated by motor vehicles independently of how much we are able to lower our reliance on private vehicle travel?
  3. What can we do to help the developing world avoid the same errors the developed world has made regarding building automobile-dominant cities?

For all three questions, lowering the vehicle population required to provide the passenger miles traveled that will be demanded in the coming decades would be a critical and likely indispensable advantage in solving the problem.

The emerging technology of autonomous vehicles offers a solution that would address all three questions: the organization of massive shared fleets that permit car ownership to be reduced to less than 20% of its projected 2050 level of four billion vehicles (i.e., 80% of the 2010 level). The robotization of motorized vehicles has value independently of whether these vehicles are shared. Vehicular autonomy will not unfold in isolation. What happens if vehicles in the 2040s were emission free from a tailpipe perspective, autonomous and if personal ownership is near-universally replaced with shared fleets? We examine these three components layered one at a time against the base of business-as-usual: our current fleet after two doublings to four billion vehicles by 2050.


When concerned about the footprint of fossil-fuel vehicles, we generally focus on the tailpipe: CO2, chemical pollutions and particulates. In general, only 50% of the total direct footprint of a motorized vehicle is its tailpipe contribution. The other 50% is in its manufacture and maintenance—mostly manufacture [Mike Berners-Lee, How Bad Are Bananas?]. Hence, if we were to make all vehicle 100% footprint-free in the tailpipe department (meaning using only 100% renewables and emitting only water), we’d cut the problem in half—but only if our vehicle population stayed constant, which is not currently the case.

The doubling time for the automobile population is twenty years. So in twenty years when the world vehicle population doubles (highly likely) and all vehicles are squeaky-clean (unlikely), you might hope that at least we broke even. We would have traded one billion dirty cars for two billion clean ones. Then the entire footprint would be in manufacturing and none in operation.

Not quite. It turns out that the value (cost) of all parking infrastructure (in the US, at least) is equivalent to the total value of all the motorized vehicles in the US [Donald Shoup, The High Cost of Free Parking]. Actually it is worse, but I approximate for simplicity. I further simplify by equating the total environmental harm caused by parking and parking infrastructure to be equivalent to that of today’s tailpipe emissions (although the harm from parking is greater). It simply does not all exhibit as global warming or air-pollution, although most does so indirectly.

There’s more. There is the environmental cost of the entire road, bridge and tunnel infrastructure. It effects are numerous and complex and they do harm in yet different ways, but I will give them the same conservative weight, just to be sure not to overestimate the harm.

The cost to the environment of 1.3 million (and growing) road deaths and a far greater number of grievous injuries each year, could again be considered, for simplicity, an equal environmental burden to each of the previous four harms.

Hence, if we will be quadrupling the total vehicle population on the globe by 2050 AND we commit only to zero out tailpipe emissions, we will have reduced the 2050 problem (slated to become 400% worse if nothing changes) by 20%—in other words the environmental problems contributed by motorized surface transportation would be only 320% worse than now.

Such a back-of-the envelope reckoning, of course is bound to be off by factor 2 at least. The problem may only become 50% worse or perhaps 700% worse. As a thought exercise, let’s see how some assumptions could play out.

Base scenario. This is a business-as-usual scenario—except that vehicle population quadruples. In this case, the total problem increases 400%, a simple linear assumption. In reality consumption usually seems to make things worse exponentially, but disruptive innovation sometimes makes them get better disruptively (or, conversely, compounds consumption [Jevons Paradox]), so a linear assumption is a both neutral and naïve. But it is a starting point.

Clean scenario. Add to the base scenario a worldwide conversion to zero-emission vehicles. Include zero-emission power-generation. This is not likely by 2050. But let’s include it, here, as a first approximation. In the Clean scenario, vehicle manufacturing, parking, road-building and road carnage continue linearly (another simplifying first approximation).

Autonomous scenario. Add to the clean scenario that by 2050 the only sorts of vehicles available are fully autonomous, that there is not a single driver left anywhere except in history movies and that road-carnage drops to zero (only a minor exaggeration as a first approximation) while manufacturing, parking, and road-building continue linearly (still a simplification).

Sharing scenario. Add to the autonomous scenario that by 2050 the universal way to access a motorized vehicle is via TNCs that provide only autonomous vehicles, and that the total worldwide quadrupled PMT demand can be satisfied with the 2010 vehicle count. Manufacturing would tick upward a bit (faster wear due to tragedy of the commons) and tick down a bit (fleet optimizations related to distribution) so we can simplistically assume manufacturing continues linear growth matching the PMT demands, i.e., 400% of 2010 output. Let’s let parking drop in half from now (i.e., 50%) since the same number of cars need less parking, but we still want to reduce deadheading so we’ll keep a lot of parking around. Let’s assume we’ll slow road-building by half of base (i.e., 200% instead of 400%) since sharing makes many road-use, scheduling and navigation optimizations possible.

Here is a figure showing these four simple scenarios played out at 2010 and 2050.

Four simple scenarios

The grossly simplified assumptions made to generate this chart, while possible, may be unlikely in the time frame, but this is the direction we want to be headed. Furthermore, there are many other elements of optimization—especially materials and additive manufacturing—that can reduce footprint.

Hence, even while my assumptions are simplifications, there are many others that when considered could make it possible (with effort) that the global footprint of surface transportation in 2050 need not be worse than it is today. There is no point in fixing the West, ignoring the Rest and hoping for the best.

Next, I will develop a second approximation with some what-if ranges.

Bern Grush 2015 05 29