Freight transport is fundamental to economic growth; however, it also contributes to the emissions of pollutants and greenhouse gases at high rates and high levels of noise near urban areas. Freight carriers’ tactical and operational decision-making in the form of eco-routing, which identifies and uses the most energy-efficient routes, can bring about desired reductions in emissions. This study explored eco-routing's potential for both freight carriers and regulators, in terms of costs, benefits, and network-wide effects. Additionally, the study assessed possible incentives like geofencing technology for carriers to eco-route by imposing a fee when carriers route trucks through geofenced, disadvantaged communities. The above goals were undertaken by focusing on the disadvantaged communities in the Southern California Association of Governments (SCAG) region.
First, the eco-routing potential from the perspective of a carrier hauling truck fleet operating between different origin-destination pairs was explored in the form of expected cost-benefits, trade-offs, and travel reliability. The benefits of eco-routing pertain to reductions in emissions. The cost of eco-routing pertains to increase in travel distance when compared with the shortest path, travel time when compared with the fastest path, and travel cost when compared with the least-cost path.
Next, this study evaluated the network-wide effects of eco-routing by developing a multi-class improved Traffic Assignment applied to the network of disadvantaged communities in the SCAG region. Specifically, the study developed the conventional routing options including shortest path (SP), fastest path (FP), and least-cost path (LCP) as well as the eco-routing option (least-emissions path (LEP)) over specific origin-destination pairs and established a corresponding multi-class traffic equilibrium to evaluate the network-wide effects of eco-routing with two vehicle classes: Light Duty Automobile (LDA), i.e., passenger cars, and Heavy-Duty Trucks (HDT). While the passenger cars were routed on the FP assignment, the trucks were routed on the SP, FP, LCP or LEP assignments.
Finally, the study also explored geofencing as a tool to protect disadvantaged communities in the region, specifically by developing two geofences, one for census tracts with high CalEnviroScreen (CES) scores - a pollution exposure index accounting for pollution burden and population characteristics, and another for the Southeast LA (SELA) region.
Results from the Cost-Benefit Analysis:
- Emission reduction benefits due to carrier eco-routing were compensated for by an increase in cost to the carrier from eco-routing. Only when the carrier routed its fleet for shortest distance did Nitrogen Oxide (NOx) eco-routing (eco-route minimizing NOx emissions) result in a higher monetary benefit than the monetary cost to the carrier.
- Fuel consumption decreased by up to 5.3 percent as a result of eco-routing (LEP assignment), depending on the pollutant being minimized through the eco-routing practice, compared to the cases of a carrier otherwise routing its fleet based on the conventional SP, FP, and LCP assignments.
Results for the Network-Wide Impacts:
- The network-wide reductions in emissions from LEP assignment were significant and as high as 10 percent for NOx in the context of the comparison between LEP and SP assignments, with a minimal number of passenger cars considered to be in the network. These findings indicate the potential of eco-routing to reduce emissions during off-peak hours with lower traffic volumes.
Results from the Proposed Geofencing Application:
- In the geofencing application for both the census tracts with high CES scores and the SELA region, emissions within the geofence reduced significantly. NOx emissions reduced by 74 percent, due to reduced truck travel within the geofence, with a minimal but equitable increase in network-wide emissions. It is worth noting that this reduction in emissions for the geofence area bought along increases in emissions elsewhere in the region, however, these impacts did not disproportionally affect other disadvantaged communities in the region.