Rising levels of atmospheric greenhouse gases (GHGs) are an increasing public health concern in the context of global climate change. Higher global temperatures linked to GHGs are projected to increase air pollution, vector-born diseases, and heat-related deaths. More frequent and severe weather events such as fires, flooding, and droughts will threaten food security, shelter, and fresh water resources in the medium and long term. Fuel combustion of on-road vehicles is one of the major sources of GHG emissions in urban environments. The three international land ports between San Diego County, California, and Baja California, Mexico, include two of the busiest passenger and commercial vehicle crossings in the world, yet they were not included in the San Diego County GHG inventory of 2006. This study estimates GHG emissions due to northbound vehicle delays at the three San Diego County-Baja California border crossings (located in San Ysidro, Otay Mesa, and Tecate) in fiscal year (FY) 2009. Carbon dioxide (CO_), nitrous oxide (N_O), and methane (CH_) emissions were quantified and expressed collectively as CO_ equivalents (CO_Eq). Estimations were based on emission rates derived from EPA's latest mobile vehicle emission simulator model, MOVES2010. Using this approach, FY 2009 emissions were approximately 80,000 metric tons (MT) of CO_Eq for all three border crossings combined, comprising 0.5% of total on-road transportation emissions in San Diego County based on the latest 2006 inventory. Of the three border crossings, the San Ysidro Port of Entry contributed the most GHG emissions (68% of total), Otay Mesa contributed significantly less (30% of total), and Tecate the least (2% of total). Heavy-duty diesel trucks at the Otay Mesa commercial crossing contributed the most on a per vehicle basis (15.3 kg CO_Eq/crossing), and vehicles using the SENTRI lanes contributed the least overall (1.1 kg CO_Eq/crossing). Of the total amount of 80,000 MT GHG emissions, 45% was due to pure idling, meaning the vehicle was completely stopped. Thus 45% of the emissions could be eliminated if idling were eliminated. Limitations of this study include lack of specific data to describe the age and type of border vehicles, conflicting commercial truck delay data, and no source of information for southbound vehicle numbers or delays. Southbound crossings were not included in this study. Northbound vehicle volumes in 2009 were significantly lower than in previous years due to an economic recession and escalated violence in Mexico that decreased tourism to and from Tijuana. Because of these limitations and the period of analysis, the results presented in this thesis are an underestimate of total border GHG emissions. Possible approaches to reducing GHG emissions for the border region include increasing SENTRI participation, decreasing border delay times, and creating a border crossing process that allows drivers to turn off their engines while waiting in line. Optimistic future projections incorporate these scenarios and represent potential target goals for 2030 GHG reduction strategies.