Via Kottke, from Preservation Magazine:
A Cautionary Tale
"Embodied energy. Another term unlovely to the ear, it's one with which preservationists need to get comfortable. In two words, it neatly encapsulates a persuasive rationale for sustaining old buildings rather than building from scratch. When people talk about energy use and buildings, they invariably mean operating energy: how much energy a building—whether new or old—will use from today forward for heating, cooling, and illumination. Starting at this point of analysis—the present—new will often trump old. But the analysis takes into account neither the energy that's already bound up in preexisting buildings nor the energy used to construct a new green building instead of reusing an old one. "Old buildings are a fossil fuel repository," as Jackson put it, "places where we've saved energy.""
Think about this applied to transportation, and the logic for the construction of new highway and transit facilities. Often the claim is made the new facility will reduce energy consumption or carbon emissions, which may be true on an operating basis, either because it switches people away from the internal combustion engine or it allows this engine to be operated more efficiently on a less congested facility. However, those analyses exclude the energy and environmental cost of construction, which is often quite large, a point which has been known for a long time, see e.g.
Lave, Charles. 1976. The Negative Energy Impact of Modern Rail-Transit Systems. Science, February 11, 1977. Vol. 195, pp. 595-596.
though the argument is not without controversy.
A similar point is the delay imposed by construction of a facility designed to reduce delay. Rarely if ever is the construction delay compared with the long-term reduction in delay. I suspect many projects would no longer be beneficial if that were included, especially if we consider the time value of money, and that current delay is worth more than downstream delay.