Most of the public discussion of the future of transportation has focused on technology. Whether in print, on TV and radio, or over the Web, we constantly hear about the latest whiz-bang way of moving passengers and cargo from place to place. We debate the relative virtues and vices of hydrogen vs. biofuels vs. petroleum energy, or of electric vs. hybrid vs. conventional drivetrains, or of trains vs. buses vs. cars. But much of the information misses the point.

Transportation technology is the least effective and most expensive tool for building a sustainable mobile future. Directing the bulk of society's attention, priority, and taxpayer dollars toward the advancement of transportation technology actually detracts from our ability to meet the challenges that we face. We need to focus our efforts to recognize which activities offer real power and leverage. In descending order, they are: 1) reducing vehicle miles traveled, 2) minimizing wasted vehicle capacity, and a distant 3) improving vehicle technology.

Transportation energy usage and emissions are extremely dependent on the type of vehicle under consideration, the exact mission the vehicle is asked to perform, and the particular type of energy used to power the vehicle. It's pretty safe to say that the energy efficiency of a "typical passenger car" in "typical service" can’t be improved by more than a factor of three unless the laws of physics are repealed. Consider a conventional (non-hybrid) vehicle which gets 25 miles per gallon (mpg) of gas on a given "passenger car" drive cycle. It is virtually impossible to design a comparable vehicle which could get the equivalent of more than 75 mpg while performing the same mission. At the absolute extreme limit of technological possibility, we might someday extract three times (3X) as much mobility per unit of energy, compared to present conventional vehicles, by improving vehicle technology. Currently-available hybrids have already achieved efficiency improvements of about 1.2X to 1.6X, mainly depending on the extent of hybridization, so an additional factor of roughly 2X remains to be explored.

The laws of physics may hit a brick wall at 3X, but society is just warming up. The driver who commutes to work alone in a 12 mpg SUV can realize a 3X improvement simply by trading the SUV for a car that gets 36 mpg. S/he can realize an additional 4X by recruiting three neighbors into a carpool, for a total improvement of 12X. If the carpoolers switch out of the car and onto a COTA bus, they may realize further gains. None of these improvements required any improved technology.

Transit planners speak frequently of the "load factor" of their systems, the quotient of seat-miles actually used divided by the total seat-miles available. High load factor means that available vehicle capacity is being used productively; low load factor implies wasted vehicle capacity. Each of the societal changes mentioned above involved improving load factor, or minimizing wasted vehicle capacity. The switch from SUV to car raises load factor by shrinking the vehicle’s capacity to more closely match the load. The carpool improves load factor using the opposite approach: raising the useful load closer to the vehicle's capacity.

The switch to mass transit involves some subtlety. A transit bus carrying 40 passengers has the same load factor as a compact car carrying four: 100 percent. In terms of passenger-miles carried per unit of energy expended, the full bus will be more efficient than the full car, but only marginally so. The bigger the vehicle, the more energy it takes to move it. In fact, because service frequency is the most important determinant of ridership, COTA runs quite a few buses at well below capacity, focusing on the load factor of the overall system, not of individual vehicles.

Because the carpool was already operating at high load factor, the carpoolers may or may not have realized improved efficiency from the vehicle they occupy by switching to COTA. Because the bus was already scheduled, society's efficiency was improved by eliminating one vehicle from the road. And a much more important shift may have occurred, as well. COTA and other transit properties perform exactly that function every hour of every day, setting up their routes and schedules so as to attract the maximum number of riders to their service. A switch out of the personal auto and onto mass transit allows high load factors to be realized on a much broader universe of impromptu trips, not just on a few predictably repeated ones.

There's another subtlety in mass transit that's highly relevant in Central Ohio, circa 2007. Efficiency improvements are multiplicative, meaning that a 2X improvement piggybacked on a 3X improvement becomes a 6X improvement. So it's entirely appropriate to think in terms of superimposing improved vehicle technology on top of improved vehicle utilization. It's appropriate to hope that COTA might someday switch from diesel buses, to diesel-hybrid buses, to electric light rail trains.

But COTA's calculation as a transit property operating a system is very different from mine as a private individual operating a vehicle. If the electric Civic performs as well as my hybrid, I'll almost certainly buy it. But a train car is not only more highly electrified than a hybrid bus, it's also three times as big. To maintain the same load factor with the larger vehicle, COTA must either a) cut frequency of operation on that route by a factor of three, or b) attract three times as many passengers to the route. Load factor determines efficiency, frequency determines ridership, and load factor moves in direct opposition to frequency. Call it COTA's Catch-22. The important thing for Central Ohio voters to remember is that, as a source of efficiency, load factor trumps technology any day. Full buses beat less-full trains, by a landslide.

The absolute most effective way to reduce the energy and emissions of motor vehicle travel is blindingly obvious: Don't travel in a motor vehicle. The dramatic increase in vehicle energy usage in the United States since the end of World War II is a direct result of the huge increase in vehicle miles traveled during that time. The greatest potential for building a sustainable transportation future lies in reducing vehicle miles traveled (VMT). There are many ways to achieve this end beyond those that also raise load factor—telecommuting and living closer to our destinations are two of the more obvious.

Telecommuting doesn't require a $25,000 home office filled with the latest electronics or even a DSL line. Just one day a month of telecommuting represents a five percent reduction in your commuting miles. Think that's trivial? Near-term, gasoline is one of the most price-inelastic commodities in the world. A five percent change in demand (or supply) will change the price by a factor of two. If everyone in the country cut their overall usage by five percent, the price per gallon could drop by half .

Similarly, if you're intent on living closer to your destinations, you don't need to buy a million dollar downtown condo or to wait for New Urbanist zoning and the development of transit-oriented, walkable communities. You don't need to move at all. Just choose to shop at the grocery that's a mile from home instead of the one that's three miles away, or to frequent the neighborhood pub instead of driving across town to the latest trendy watering hole. Think globally, act personally.

To minimize your energy usage and emissions from travel in motorized vehicles, minimize your travel in motorized vehicles and use vehicles productively. And finally, if the spirit moves, lower your energy consumption and emissions by buying the latest and greatest "green" vehicle.