This Guardian article about efforts to reduce the environmental and energy impacts of road construction and maintenance (“America has 10% of the planet’s roads and building each mile of freeway uses as much energy as 200 US homes in a year”) got me to thinking about the proportion of US energy used by transportation.
The usual energy-consumption-by-sector statistics we see are something like this pie chart from this DOE report.
The problem with this perspective is that it only considers the operational consumption of energy. Manufacture of vehicles and construction and maintenance of roads is not included. The above article made me wonder specifically about the relative amount of energy consumed by the latter.
With a little research, I found an article (Hybrid Life-Cycle Inventory for Road Construction and Use. G. J. Treloar, P. E. D. Love, and R. H. Crawford. ASCE Journal of Construction Engineering and Management. January/February 2004) that answers my questions. This chart summarizes the conclusions of the article (the caption is from the article).
Life-cycle energy attributable to road construction and use. The step jumps in the line for vehicle manufacture and maintenance represent complete vehicle replacement at 15 year intervals. Increases in road life-cycle energy are due to the energy embodied in materials used for maintenance. Continuously reinforced concrete, CRC; fulldepth asphalt, FDA; deep-strength asphalt, DSA; deep-strength asphalt on bounded subbase, DSAB; plain concrete, PC; composite, asphalt, and concrete, Comp; granular, G; and asphaltic concrete on bounded subbase, ACB.
From this perspective, it looks like the total life-cycle energy cost (and carbon footprint) of road-based motor-vehicle-oriented transportation is 50% to 75% greater than the simplified energy-use-by-sector perspective offered by DOE. Of course, most of the “industrial” sector could probably be divvied up between the other sectors from a life-cycle perspective.