In a recent study, researchers argue that many analyses of the impact of GHG (greenhouse gas) emissions overlook those GHG's emitted in constructing and maintaining the transportation infrastructure.  For example, based on passenger kilometers traveled, the researchers found that off-peak urban bus services were more carbon-intensive than commercial aircraft flights.  When an assessment includes, for example, vehicle production and maintenance, the construction and maintenance of infrastructure, and the fuel production requirements to support all of these various activities, then a different picture emerges.  To illustrate their point, the researchers compared the aforenoted bus travel and aircraft flight.

The key to reducing GHG emissions, the researchers note, is to promote increased occupancy of vehicles, and to examine options in terms of the entirety of their effects, not merely tailpipe emissions.

The study can be found at http://www.iop.org/EJ/article/1748-9326/4/2/024008/erl9_2_024008.pdf?request-id=b92df71a-8f2c-4455-a783-9ff30fb6b8ce.