Freight on a Low-Carbon Diet: Accessibility, Freightsheds, and Commodities.

The freight infrastructure network (e.g., roads, railways, waterways, etc.) is the backbone of nearly all trade partnerships in the United States and abroad. The manner in which the individual portions of its constituent parts are interrelated or arranged plays an important role for determining the environmental footprint of goods moved within the network. Herein, we compare the spatial distribution of potential consumer-producer exchanges (i.e., accessibility) under varying greenhouse gas (GHG) budgets or preferences for minimal transportation-related GHG emissions. We conduct case studies using two freight modes (truck and intermodal rail) for two representative commodities: meat/seafood and paper articles. Results across all counties in the United States indicate that the geographic area in which trade is possible, given a GHG budget, varies by transportation mode, location, and commodity. Our results suggest that intermodal terminal availability is an important determinant of low-GHG accessibility. Since only a fraction of road-to-rail terminals accommodate meat/seafood (4.9%) and paper (0.7%), the United States could increase its expected GHG savings associated with truck-to-rail mode-switching policies by 70% (+20 kg CO2,e/ton for meat/seafood) and 310% (+30 kg CO2,e/ton for paper) by upgrading current terminals to allow the exchange of all types of goods.

Bias of averages in life-cycle footprinting of infrastructure: truck and bus case studies.

The life-cycle output (e.g., level of service) of infrastructure systems heavily influences their normalized environmental footprint. Many studies and tools calculate emission factors based on average productivity; however, the performance of these systems varies over time and space. We evaluate the appropriate use of emission factors based on average levels of service by comparing them to those reflecting a distribution of system outputs. For the provision of truck and bus services where fuel economy is assumed constant over levels of service, emission factor estimation biases, described by Jensen's inequality, always result in larger-than-expected environmental impacts (3%-400%) and depend strongly on the variability and skew of truck payloads and bus ridership. Well-to-wheel greenhouse gas emission factors for diesel trucks in California range from 87 to 1,500 g of CO2 equivalents per ton-km, depending on the size and type of trucks and the services performed. Along a bus route in San Francisco, well-to-wheel emission factors ranged between 53 and 940 g of CO2 equivalents per passenger-km. The use of biased emission factors can have profound effects on various policy decisions. If average emission rates must be used, reflecting a distribution of productivity can reduce emission factor biases.