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Transportation Network Carbon Accounting: A Protocol for Greenhouse Gas Emission Calculations

When it comes to personal transport decisions, bus vs train vs car vs air, the contributing factors and trade-offs are known: time, cost, capacity, convenience. The cost of the trip is divided among the passengers often at the expense of convenience. The duration of the trip can be shortened for an increase in cost. The same is largely true when it comes to freight, but whether deciding how to travel to a wedding or how to get a shipment to a customer warehouse, emissions do not usually come to mind. The global pressure to lessen the impact of climate change are starting to shift the way transport decisions are made.

As more companies develop corporate green initiatives logistics operations, and particularly transportation emissions, have become increasingly targeted for reduction. Roughly 8% of all greenhouse gas emissions are attributed to non-passenger transport and companies largely control how their product gets to customers. With this control many target transportation as a potential means to impact greenhouse gas emissions. Unlike freight cost calculations, where pricing structures have been established for each mode, emissions calculation methods are varied and often disagreeing. A collaborative study between Massachusetts Institute of Technology (MIT), the Environmental Protection Agency (EPA), Estes Express, Yellow, and C.H. Robinson as part of the EPA SmartWay program utilized data from the carriers’ terminals and LTL shipments to provide a path forward through the fog (EPA, April 2021).

Straight-line shipment emissions calculations are simpler than others with multiple unknown legs. When a straight-line truckload shipment leaves the dock it is sent directly to the destination, the over the road miles relate directly to the emissions and work required to make the delivery. The emission rates for truckload miles are backed into via fuel efficiency standards. Intermodal miles and ocean shipping are largely the same. Fuel efficiencies are well understood and applying them to shipments calculating network emissions becomes largely an effort to tabulate detailed shipping records. Similar to the physics concept of “work”, displacement * force, emissions are calculated on weight * distance. A factor for deadhead miles is then added which represents the mileage the delivery vehicle travels empty before picking up another load. The Smartway study puts this near 10% of roadway miles based on data shared from actual ESTES Express shipments. While TL, ocean, and rail shipment emissions are relatively simple to calculate, Less-than-truckload (LTL) shipments are a different story.

LTL shippers hand over control and visibility, to a lesser extent, of their freight at the dock. Unlike TL shipments which go directly to the destination, LTL shipments move through a network of LTL terminals before being put on a delivery route for final delivery. Additional assumptions need to be made when shippers have limited visibility to the actual shipping road miles (Veloso de Aguiar et al. 2014). There are some important differences between LTL shipping and TL shipping:

  • Equipment – LTL route trucks are often slightly smaller and more fuel efficient than long haul tractors.
  • Capacity – trailer utilization is lower for shorter shipments
  • Pickup & Delivery (P&D Miles) – Regional differences in population density contribute to LTL route mileage differences

LTL shipment emissions calculations can be separated into two portions, linehaul and P&D mileage. Linehaul portion relates to the transfers between terminals which largely operate as full truckload shipments. Linehaul mile emissions are calculated the same way other TL shipments are calculated, on a weight * distance basis. The emissions of the trip are split proportionally based on the weight of the shipment unlike P&D miles which are variable based on the number of stops on the route. Based on data provided by Estes Express P&D miles per shipment vary based on geographic region (Veloso de Aguiar et al. 2014). The regional differences are included below:

Region Avg P&D Miles per Shipment Std Dev P&D Miles per Shipment P&D Mile Avg+Std Dev
NE 5.06 2.43 7.49
NM 6.33 3.68 10.01
NW 6.72 4.58 11.3
SE 4.83 1.84 6.67
SM 7.16 3.36 10.52
SW 6.57 3.74 10.31


Region States


Every shipment on the LTL route causes the entire vehicle to travel additional miles based on the regional average. The P&D portion of the emissions is based on the average P&D miles and the cargo weight of the route vehicle which also varies. It is rare that the various shipments on an LTL delivery route add up to 100% of the trailer capacity. For shipments less than 300 miles the trailer is often only 75% full whereas shipments greater than 300 miles are often 85% full. Depending on the specific product density and cargo weight of a full truckload the emissions rate per mile may be slightly higher or lower. The linehaul and P&D portions of the LTL shipment emissions are added together as the total emissions.

As a part of the Network Analysis workflow at St. Onge Company we often collect shipment records to baseline logistics spend and prepare optimization models. This is data can also be used to create emissions profiles. Additional effort as a part of network analysis can include baselining network emissions to compare against network alternatives. The first step to meeting emissions reduction goals is baseline the current state.


(EPA, April 2021) Case Study: Public-Private Collaboration Validates Methodology, Produces User-Friendly Emissions Calculator for Guiding Sustainable Freight. EPA.

G.Veloso de Aguiar, M,A. Woolard (2014) Estimating Carbon Emissions from Less-than-Truckload (LTL) Shipments
—Austin Chacosky, St. Onge Company

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