The paper offers an assessment of the environmental impact of trade liberalization on the cross-border trucking sector in North America. Specific policies in the realm of transportation, environment and trade are investigated with data directly related to the time of implementation that varied across ports on each of the two international borders in North America subsequent to the North American Free Trade Agreement (NAFTA). The data on truck flows, wait times, air quality and trade value are analyzed using econometrics for quantitative analysis. Results show various policies do have a positive impact on reducing air emissions through changes in trucking characteristics (technology, patterns) in particular ports where they have been implemented.