11.4 Sustainable transportation: accessibility, mobility, and  (Page 4/12)

However, simply producing more fuel-efficient vehicles is not sufficient when we consider the embodied energy    of the car itself. It takes a lot of energy to make a car, especially in the modern "global assembly line," where parts come from multiple countries for final assembly, and that energy becomes "embodied" in the metal, plastic, and electronics of the car. A study in Europe found that unless a car is over 20 years old, it does not make sense to trade it in for a more efficient one because of this embodied energy ( Usón et al., 2011 ). Most Americans trade in their cars after about a third of that time. A related concept is true for electric cars. In their daily usage, they generate zero carbon emissions, but we should also consider the source of power used to recharge the vehicle. In most parts of the U.S., this is coal, and therefore the emissions savings are only about 30% over a traditional vehicle ( Marsh, 2011 ).

If transportation is a derived demand, another way to meet our current transportation needs is by changing the demand. There are two related aspects to this. First, there is a clear causal link between having more transportation infrastructure and more miles traveled on that infrastructure, and greater economic growth. This is true between regions of the world, between individual countries, and between people and regions within countries. This causal connection has been used as a reason to finance transportation projects in hundreds of different contexts, perhaps most recently in the American Reinvestment and Recovery Act that distributed federal funds to states and localities to build infrastructure in the hopes that it would create jobs. Policymakers, businesspeople, and citizens therefore all assume that we need more transportation to increase economic growth.

However, it is also true that more transportation does not automatically mean more economic growth: witness the state of West Virginia, with decades' worth of high-quality road infrastructure bestowed upon it by its former Senator Robert Byrd, but still at the bottom of economic rankings of states. Furthermore, at some point a country or region gains no significant improvements from additional infrastructure; they have to focus on making better use of what they already have instead. We therefore need to decouple economic growth from transportation growth ( Banister and Berechman, 2001 ). We can substitute telecommunication for travel, work at home, or shop online instead of traveling to a store (although the goods still have to travel to our homes, this is more efficient than each of us getting in our own cars). We can produce the goods we use locally instead of shipping them halfway around the world, creating jobs at home as well as reducing resource use and emissions. All of these options for decoupling are ways to reduce the demand for transportation without also reducing the benefits from the activities that create that demand.

The other way to think about changing the derived demand of transportation is via the concepts of accessibility    and mobility    . Mobility is simply the ability to move or to get around. We can think of certain places as having high accessibility: at a major intersection or freeway exit, a train station, etc. Company headquarters, shopping malls, smaller businesses alike decide where to locate based on this principle, from the gas stations next to a freeway exit to the coffee shop next to a commuter rail station. At points of high accessibility, land tends to cost more because it's easier for people to get there and therefore more businesses or offices want to be there. This also means land uses are usually denser: buildings have more stories, people park in multi-level garages instead of surface lots, etc.