The COVID-19 pandemic has been a worldwide issue that transit agencies are still struggling to find cost-efficient solutions to. Upgrading the filters used on trains and buses to reduce the airborne transmission of the SARS-CoV-2 virus as well as other infectious viruses, such as influenza, may be an effective, cost-efficient way of containing the very small, hard-to-filter droplet and aerosol particles that these viruses may travel within. One way to improve transit vehicle air quality and safety is to upgrade the current MERV-rated filters to higher-rated ones such as a MERV 13 filter. This study looked at quantifying the upgraded filters’ performance, focusing on their efficacy over time and comparing them to a MERV 8 filter. Filter performance was investigated using sodium chloride (NaCl) particles and Arizona Road Dust (ARD) particles to determine the filter collection efficiency. A Grimm MiniWras and Aerodynamic Particle Sizer was used to compare the number concentrations (#/L) of particles upstream and downstream of the filter. The filter testing data confirm that MERV-13 filters have better filtration efficiency compared to MERV-8 filters but the filter performance varies depending on the age of the filter (i.e., its loading), particle type, and particle properties (charged vs. neutralized).