Opportunities to Reduce Vehicle Emissions at Land Border Crossings between the US and Mexico: Case Study at the Mariposa Port of Entry

Vehicle border crossings between the United States and Mexico generate significant amounts of air pollution, which can pose health threats to personnel at the land ports of entry (POEs) as well as drivers, pedestrians, and... [ view full abstract ]

Vehicle border crossings between the United States and Mexico generate significant amounts of air pollution, which can pose health threats to personnel at the land ports of entry (POEs) as well as drivers, pedestrians, and local inhabitants. Although these health risks could be substantial, there is little previous work quantifying detailed emission profiles at POEs.  The Mariposa POE is one of the busiest POEs along the US-Mexico border with over 11,000 vehicles processed per day.  This often creates long queues of vehicles waiting to enter the United States.  Furthermore, the vehicle traffic at the POE is expected to increase over the coming decades.  The POE borders Nogales, Arizona (US) and Nogales, Sonora (Mexico), with a combined population of nearly 235,000. Using the Mariposa POE as a case study, we analyzed light-duty and heavy-duty vehicle emissions with the objective of identifying effective emission reduction strategies such as inspection streamlining, physical infrastructure improvements, and fuel switching. We used historical traffic statistics as well as observed field data to establish a simulation model of vehicle movement in VISSIM. We developed four simulation scenarios with varied congestion levels to represent real-world seasonal changes in traffic volume. Four additional simulations captured varying types of expedited processing procedures. The VISSIM output was analyzed using the EPA’s MOVES emission simulation software for conventional air pollutants. For the highest congestion scenario, which includes a 200% increase in vehicle volume, total emissions increase by around 460% for PM_2.5 and NO_x, and 540% for CO, SO₂, GHGs, and NMHC compared to uncongested conditions in a two-hour period. Expedited processing and queue reduction can reduce emissions in this highest congestion scenario by as much as 16% for PM_2.5, 18% for NO_x, 20% for NMHC, 7% for SO₂ and 15% for GHGs and CO. We also examined other potential mitigation strategies such as fleet upgrades, fuel switching, and fuel upgrades.  Adoption of some or all of these changes would not only reduce emissions at the Mariposa POE, but would have air-quality benefits for nearby populations in both the US and Mexico. Fleet-level changes could have far-reaching improvements in air quality on both sides of the border.